cp's OEIS Frontend

A376830 Numbers k such that tau(k + tau(k)) = tau(k) + tau(tau(k)), where tau = A000005.

%I A376830 #31 Oct 07 2024 01:27:28
%S A376830 1,13,19,31,37,53,67,83,88,89,109,113,127,131,139,152,157,181,190,199,
%T A376830 211,225,233,251,257,263,276,286,293,307,317,337,344,353,379,389,401,
%U A376830 406,409,443,449,467,479,487,491,499,503,509,536,541,557,563,571,577,587,612,631,642,647,653,658,677
%N A376830 Numbers k such that tau(k + tau(k)) = tau(k) + tau(tau(k)), where tau = A000005.
%H A376830 Robert Israel, <a href="/A376830/b376830.txt">Table of n, a(n) for n = 1..10000</a>
%e A376830 a(9) = 88 is a term because tau(88) = 8, tau(8) = 4 and tau(88 + 8) = tau(96) = 12 = 8 + 4.
%p A376830 filter:= proc(k) uses numtheory; local s;
%p A376830  s:= tau(k);
%p A376830  tau(k+s) = s + tau(s)
%p A376830 end proc:
%p A376830 select(filter, [$1..1000]);
%t A376830 Select[Range[680],DivisorSigma[0,#+DivisorSigma[0,#]]==DivisorSigma[0,#]+DivisorSigma[0,DivisorSigma[0,#]] &] (* _Stefano Spezia_, Oct 06 2024 *)
%Y A376830 Cf. A000005, A376831, A376843, A376844, A376848, A376849, A376851. Includes A115093.
%K A376830 nonn
%O A376830 1,2
%A A376830 _Robert Israel_, Oct 06 2024