I have written on the Gayatri Mantra, the most sacred of the Mantras of Hindus, quite a few articles,

its efficacy in realizing The Reality and its effect in warding off evil and its power to sharpen the Intellect and bestowing Prosperity.

I have also written about the number of letters in the Gayatri Mantra.

Based on Intonation the Gayatri Mantra has Twenty our letters

Now, who are the Rishis of the Gayatri Mantra and the Chief Rishi who released the Gayatri Mantra?

The Rishi who revealed the Gayatri Mantra is Sage Visvamitra.

The Rishis, according the Nyasa we recite for the Gaytri are seven in number..

They are,

Atri,

Bhrigu,

Kutsa,

Vasishta,

Gautama,

Kasyapa and

Angirasa.

But the Devi  Bhagvatham states there are twenty our Rishis

The Risis, in due order, are

(1) Vâma Deva,

(2) Attri,

(3) Vas’istha

,(4) S’ukra,

(5) Kanva,

(6) Parâs’ara,

(7)  Vis’vamitra,

(8) Kapila,

(9) S’aunaka,

(10) Yâjñavalkya,

(11) Bharadvâja,

(12) Jamadagni,

(13) Gautama,

(14) Mudgala,

(15) Vedavyâsa,

(16) Lomas’a,

(17) Agastya,

(18) Kaus’ika,

(19) Vatsya,

(20) Pulastya,

(21) Mânduka,

(22)  Durvâsâ,

(23) Nârada and

(24) Kas’yapa.

( 12th Book,Chapter I, Slokas 1 to 7)

It may be noted that one Rishi seems to have been assigned to One tone(for one syllable)

And Agastya seem to find a place a well.

There is Kausika, apart from Viswamitra.

Viswamitra was known as Kausika when he was a King.

I am checking on this Kausika as I feel he is another Rishi.

Reference and citation.

 Devi Bhagavtham