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

1,2

Links

Table of n, a(n) for n=1..74.

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A138009, A067004.

Sequence in context: A117248 A373624 A343292 * A146288 A244361 A199424

Adjacent sequences: A079785 A079786 A079787 * A079789 A079790 A079791

Keyword

nonn

Author

Amarnath Murthy, Feb 03 2003

Extensions

More terms from Ryan Propper, Mar 30 2006

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

Status

approved