cp's OEIS Frontend

A274790 Numbers in the range of the sum of odd divisors function.

%I A274790 #29 Jul 08 2016 09:52:43
%S A274790 1,4,6,8,12,13,14,18,20,24,30,31,32,38,40,42,44,48,54,56,57,60,62,68,
%T A274790 72,74,78,80,84,90,96,98,102,104,108,110,112,114,120,121,124,128,132,
%U A274790 133,138,140,144,150,152,156,158,160,164,168,174,176,180,182,183
%N A274790 Numbers in the range of the sum of odd divisors function.
%C A274790 Numbers which appear in A000593.
%C A274790 Possible values for the sum of odd divisors of the positive integers, in increasing order. - _Omar E. Pol_, Jul 06 2016
%H A274790 Robert Israel, <a href="/A274790/b274790.txt">Table of n, a(n) for n = 1..10000</a>
%p A274790 N:= 10000:# to get all terms <= N
%p A274790 p:= 3:
%p A274790 S:= {1}:
%p A274790 while p < N do
%p A274790   S:= map(s -> seq(s*(p^(e+1)-1)/(p-1), e=0..ilog[p](1+N*(p-1)/s)-1), S);
%p A274790   p:= nextprime(p);
%p A274790 od:
%p A274790 sort(convert(S,list)); # _Robert Israel_, Jul 06 2016
%t A274790 Union@ Table[Total@ Select[Divisors@ n, OddQ], {n, 200}] (* _Michael De Vlieger_, Jul 07 2016 *)
%o A274790 (PARI) list(lim)=lim\=1; my(v=[1]); forprime(p=3,lim\4, my(t,u=v,lm); for(e=1,logint(lim,p), t=(p^(e+1)-1)/(p-1); lm=lim\t; u=concat(u,select(k->k<=lm,v)*t)); v=Set(u)); Set(concat(v, apply(p->p+1, primes([lim\4,lim-1])))) \\ _Charles R Greathouse IV_, Jul 06 2016
%Y A274790 Cf. A000593, subsequence of A002191, A274793 (complement).
%K A274790 nonn
%O A274790 1,2
%A A274790 _Timothy L. Tiffin_, Jul 06 2016