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A079788
a(n) = count of numbers <= n for which the number of divisors is also <= tau(n).
2
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
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
Sequence in context: A117248 A373624 A343292 * A146288 A244361 A199424
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