A324255 - OEIS

%I #10 Mar 01 2019 03:00:56

%S 23,14999,34673,55373,2056961,2458187,4586987,5174363,6204767,

%T 15788453,20699927,22239647,25748273,43428947,53636627,74005637,

%U 92626307,132253139,134131379,158486747,167677187,183614987,307412933,385042487,413859143,418168343,683772017

%N Lesser of super amicable pair m < n defined by sigma(sigma(m)) = sigma(sigma(n)) = m + n.

%C The larger numbers in each pair are in A324256.

%C Analogous to A002025 as A019279 is analogous to A000396.

%e (23, 37) are the first pair since sigma(sigma(23)) = sigma(sigma(37)) = 60 = 23 + 37.

%t seq={}; s[n_]:=DivisorSigma[1,DivisorSigma[1,n]]-n; Do[m=s[n];If[m>n && s[m]==n, AppendTo[seq, n]], {n,1,60000}]; seq

%o (PARI) f(n) = sigma(sigma(n)) - n;

%o lista(nn) = {for (n=1, nn, my(fn = f(n)); if ((fn > n) && (f(fn) == n), print1(n, ", ")););} \\ _Michel Marcus_, Feb 20 2019

%Y Cf. A000203, A000396, A002025, A019279, A045613 (unitary analog), A051027, A324256.

%K nonn

%O 1,1

%A _Amiram Eldar_, Feb 19 2019