In the same manner that I call out the name of Hashem, ascribe greatness to our God

At the start of Haazinu:

ג כִּי שֵׁם ה', אֶקְרָא: {ס} הָבוּ גֹדֶל, לֵאלֹהֵינוּ. {ר}

3 For I will proclaim the name of the LORD; ascribe ye greatness unto our God.

But as we will see, Chazal midrashically interpret this as: In the same manner that I call out the name of Hashem, so shall you ascribe greatness to our God.

Targum Pseudo-Yonatan appears to make reference to this when he says:

Woe to the wicked who make memorial of the Holy Name with blasphemies. Wherefore Mosheh, who was the Doctor of Israel, would not permit himself to pronounce the Holy Name until he had dedicated his mouth at the beginning of his hymn with eighty and five letters, making twenty and one words, and afterwards be spake: In the Name of the Lord I invoke you, O house of Israel, to ascribe glory and greatness before our God.

as does Targum Yerushalmi which states:

Mosheh the prophet said: Woe to the wicked who make memorial of the Holy Name with blasphemies. For it is not possible even to one of the highest angels to utter that Name rightly until that they have said, Holy, Holy, Holy thrice. And from them did Mosheh learn not to utter that Name openly until he should have dedicated his mouth with twenty‑one words which consist of eighty-five letters; and so explained he and said: Hear, ye heavens, and I will speak; for it is the Name of the Lord. Mosheh the prophet said: O people of Israel, I invoke you, in the Name of the Lord, to give glory, praise, and highest exaltation unto God.

This is based on a derasha found in the Sifrei. While Rashi cites a different lesson brought down in Sifrei, we also have:

כי שם ה׳ אקרא נמצינו למדים שלא הזכיר משה שמו של מקום אלא לאחר כ״א דבר.

ממי למד ממלאכי השרת שאין מלאכי השרת מזכירים את השם אלא לאחר ג׳ קדושות

שנאמר וקרא זה אל זה ואמר קדוש קדוש קרוש ה׳ צבאות אמר משה די שאהיה בפחות

משבעה כמלאכי השרת• והרי דברים ק"ו ומה משה שהוא חכם חכמים גדול שבגדולים

לא הזכיר שמו של מקום אלא לאחר כ״א דבר המזכיר, שמו של מקום בחנם עאכ״ו

Perhaps the way this is taken is as a condemnation of those who take Hashem's name in vain, bechinam. Unless bechinam means without anything as introduction, which is quite plausible.

At any rate, the idea is that the word YKVK only occurs after 21 words into Haazinu. And, I think, the derasha is as I described it above, that one should ascribe greatness to Hashem in the same manner that Moshe did it in Haazinu.

Chizkuni details all of this, first citing the Targum Yerushalmi and then the Sifrei.

That Moshe said that "it is enough for me that I be after 7 {times} the angels." And then he appears to take pains to explain it, even though in our texts of the Sifrei, at the least, this explanation is more or less explicit.

But Chizkuni goes on to elaborate that therefore, the Sages instituted the whole lead-in to kedusha, such that we, too, arrive at the 21 word count before saying

YKVK, or rather, Adonai. Thus, he gives the daily introduction as nekadesh shimcha baOlam... And if we count the words he brings down, it amounts to precisely 21. Of course, we have a slightly different version. We say nekadesh et shimecha baOlam. But then, while Chizkuni has vechen katuv, we have kakatuv, thus losing a word, such that the count stands at 21.

In the kedusha of the Yotzer, which is (she-bat) {or does he mean Shabbat?} one of 85 letters. And he gives the nusach of the kedusha, which also has 21 words. {The flow here makes his intent a bit unclear to me. I wasn't able to count 85 letters, but only 82. But I would that is because he consistently writes kadosh as chaser, where it is meant to be written malei. Which would bring us to 84, but I suppose I either missed one letter or another word should be malei. Also, did he mean to refer to the seder of kedusha in the beracha of yotzer or separately?} Though ours is more expansive. And so too during Musaf, we only mention it after 85 letters. And its order is keter yitnu lecha hamonei maalah im amecha yisrael kevutzei mata, yachad kedusha lecha yeshaleshu, kakatuv al yad neviecha vekara zeh el zeh veamar, kadosh kadosh kadosh.

But in this one, we reach a 21 count before the first kadosh! So word count is not the issue, but rather letter count, which indeed is 85, since kadosh is spelled malei. Luckily, Targum makes it about 85 letters as well, such that it works out. Sifrei doesn't explicitly mention this.

Also, a word about keter. In our version, we have the introduction of keter yitenu lecha Hashem Elokeinu. If the purpose is a 21 word buffer, or an 85 letter buffer, we have entirely undermined ourselves by front-loading the Shem Hashem.

Though he mentions Yotzer in passing, he gives what I think we call the kedusha of Shabbat. Maybe he is giving both there.

Ginsberg, in Geonica, volume 1, discusses the possibility that many of these kedushot are post-Talmudic in origin; except for that of Yotzer, which is early. I believe this means the kedusha in Yotzer Or after Barechu. This may or may not have application to the above.

I don't think that Chizkuni's insight in necessary. Even if we are basing ourselves on Moshe, based on this derasha, we do not necessarily have to match him in the precise number of letters or words. This is just what Moshe did. Despite the kal vachomer. And this is assuming they even were talking about kedusha in Sifrei.