A079788 a(n) = count of numbers <= n for which the number of divisors is also <= tau(n).

1, 2, 3, 4, 4, 6, 5, 8, 7, 10, 6, 12, 7, 13, 14, 15, 8, 18, 9, 20, 17, 18, 10, 24, 13, 21, 22, 27, 11, 30, 12, 30, 25, 26, 27, 36, 13, 29, 30, 39, 14, 41, 15, 39, 40, 33, 16, 48, 20, 44, 36, 46, 17, 52, 38, 54, 39, 40, 18, 60, 19, 43, 54, 55, 44, 63, 20, 57, 46, 67, 21, 72, 22, 49

Offset: 1

Author

Amarnath Murthy, Feb 03 2003

Keywords

• nonn

Examples

			a(7) = 5 as 1, 2, 3, 5 and 7 qualify for the count.
		

Crossrefs

Cf. A138009, A067004.

Programs

Mathematica

Do[s = 0; For[i = 1, i <= n, i++, If[DivisorSigma[0, i] <= DivisorSigma[0, n], s++ ]]; Print[s], {n, 1, 50}] (* Ryan Propper, Mar 30 2006 *)

PARI

for(n=1,200,m=0;sn=sigma(n,0);for(i = 1,n,if(sigma(i,0)<=sn,m++));print1(m",")) \\ Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

Extensions

More terms from Ryan Propper, Mar 30 2006

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007