In all the four Veda Samhitās there are several hymns dealing with numbers. The decimal system for positive integers had become popular even in those days.
Rigveda Samhita
The names for the numbers one to nine found in Rigveda are eka, dve, tri, chatur, pancha, shat, sapta, asta, nava. The names for ten, twenty,……, ninety occur in RV (2.18.5-6). The intermediate numbers have appropriate names. For instance ninety-four is termed four plus ninety. Nineteen is expressed one less than twenty etc. RV (3.9.9) has number 3339 spelled as three thousand, three hundred and thirty nine. Rigveda has more than a hundred references to numbers.
Yajurveda Samhita
The Shukla Yajurveda (17.2) [Chapter 17, mantra 2] mentions numbers in ascending powers of ten, including ten thousand, ayuta; hundred thousand, niyuta; million, payuta; ten million, arbuda; hundred million, nyarbuda; billion, samudra; ten billion, madhya; hundred billion, anta; thousand billion, parardha. Similar list in Krişhņa Yajurveda (4.4.11).
It is not out of place to remark that the highest number known ancient greeks is ten thousand.
We give below the listing of the ten anuvākās in Book or kānda 7, prapāţhaka 2 i.e., (7.2) in Krişhņa Yajurveda.
(7.2.11): numbers in sequence
(7.2.12): odd (or uneven) numbers
(7.2.13): even numbers
(7.2.14): numbers 3,5,etc.,
(7.2.15): numbers 4,8,…etc.,
(7.2.16): numbers 5,10,…etc.,
(7.2.17): numbers 10,20,…etc.,
(7.2.18): numbers 20,40,…etc.,
(7.2.19): numbers 50,100,…etc.,
(7.2.20): numbers 100,1000,…upto ten raised to the power of eleven.
Atharva Veda Samhita
The hymns (6.25.1, 6.25.2 and 6.25.3) and (7.4.1) specially emphasise the common relationship between one and ten, three and thirty, five and fifty, nine and ninety, clearly indicating that these persons had a good grasp of the basics of decimal system for positive integers.