cp's OEIS Frontend

A275660 Numbers n such that sigma(n) = Sum_{j=1..k} d(n^j) for some k, where sigma(n) is the sum of the divisors of n and d(n) is the number of divisors of n.

%I A275660 #18 Feb 21 2024 08:27:23
%S A275660 1,13,19,34,43,53,58,89,103,151,229,251,254,329,341,349,404,433,463,
%T A275660 593,674,701,739,859,1033,1223,1429,1483,1506,1670,1709,1826,1846,
%U A275660 1886,1889,1948,1951,2067,2091,2143,2255,2308,2431,2699,3001,3079,3319,3739,4003,4093
%N A275660 Numbers n such that sigma(n) = Sum_{j=1..k} d(n^j) for some k, where sigma(n) is the sum of the divisors of n and d(n) is the number of divisors of n.
%C A275660 The primes in this sequence are A124199. - _Robert Israel_, Feb 20 2024
%H A275660 Robert Israel, <a href="/A275660/b275660.txt">Table of n, a(n) for n = 1..2000</a>
%e A275660 d(53^1) + d(53^2) + d(53^3) + d(53^4) + d(53^5) + d(53^6) + d(53^7) + d(53^8) + d(53^9) = 54 = sigma(53).
%p A275660 P:= proc(q) local a,k,n;
%p A275660 for n from 1 to q do a:=sigma(n); k:=0;
%p A275660 while a>0 do k:=k+1; a:=a-tau(n^k); od;
%p A275660 if a=0 then print(n); fi; od; end: P(10^9);
%Y A275660 Cf. A000005, A000203, A124199, A270389, A275661.
%K A275660 nonn
%O A275660 1,2
%A A275660 _Paolo P. Lava_, Aug 04 2016