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A079788 a(n) = count of numbers <= n for which the number of divisors is also <= tau(n). 2

%I

%S 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,

%T 27,11,30,12,30,25,26,27,36,13,29,30,39,14,41,15,39,40,33,16,48,20,44,

%U 36,46,17,52,38,54,39,40,18,60,19,43,54,55,44,63,20,57,46,67,21,72,22,49

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

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

%t 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 *)

%o (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

%Y Cf. A138009, A067004.

%K nonn

%O 1,2

%A _Amarnath Murthy_, Feb 03 2003

%E More terms from _Ryan Propper_, Mar 30 2006

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

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Last modified September 18 04:22 EDT 2021. Contains 347508 sequences. (Running on oeis4.)