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A228372 Number of nontrivial divisors in the first n composites. 1

%I #9 Nov 10 2017 09:23:20

%S 1,3,5,6,8,12,14,16,19,23,27,29,31,37,38,40,42,46,52,56,58,60,62,69,

%T 71,73,79,85,89,93,95,103,104,108,110,114,120,122,128,130,132,142,144,

%U 148,153,155,161,165,167,173,183,185,189,193,195,201,209,212,214,224,226

%N Number of nontrivial divisors in the first n composites.

%C Also, positions where values change in A228363.

%C Partial sums of A144925.

%H Harvey P. Dale, <a href="/A228372/b228372.txt">Table of n, a(n) for n = 1..10000</a>

%t Accumulate[DivisorSigma[0,#]-2&/@Select[Range[100],CompositeQ]] (* _Harvey P. Dale_, Nov 10 2017 *)

%o (PARI) L=listcreate();for(n=1,1000,if(!isprime(n),listput(L,n)));co=Vec(L);s=0;for(n=2,100,s=s+numdiv(co[n])-2;print1(s,","))

%K nonn

%O 1,2

%A _Ralf Stephan_, Aug 21 2013

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Last modified March 19 09:40 EDT 2024. Contains 370981 sequences. (Running on oeis4.)