cp's OEIS Frontend

A364860 Greater of a pair of S-amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A364858(k).

%I A364860 #7 Aug 12 2023 02:29:08
%S A364860 198,1210,2220,6368,10856,66992,525915,652664,5495264,7684672,
%T A364860 13727466,16150628,25640096,26138475,28128368,33642028,34380688,
%U A364860 40803868,133471275
%N A364860 Greater of a pair of S-amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A364858(k).
%C A364860 S-amicable numbers are analogous to amicable numbers (A002025/A002046) as S-perfect numbers (A118372) are analogous to perfect numbers (A000396).
%C A364860 The terms are ordered according to their lesser counterparts (A364859).
%F A364860 a(n) = A364858(A364859(n)).
%e A364860 198 is a term since A364858(198) = 186 < 198, and A364858(186) = 198.
%t A364860 seq[nmax_] := Module[{s = {1}, sum, sum2, am = {}, ak}, Do[sum = Total[Select[Divisors[n], MemberQ[s, #] &]]; If[sum <= n, AppendTo[s, n]; If[sum < n, sum2 = Total[Select[Most[Divisors[sum]], MemberQ[s, #] &]]; If[sum2 == n, AppendTo[am, n]]]], {n, 2, nmax}]; am]; seq[10^4]
%o A364860 (PARI) lista(nmax) = {my(c = 0, s, s2); for(n=2, nmax, s = sumdiv(n, d, !bittest(c, d)*d) - n; if(s > n, c+=1<<n); if(s < n, s2 = sumdiv(s, d, ((d<s)&&!bittest(c, d))*d); if(s2 == n, print1(n,", "))));} \\ after _M. F. Hasler_ at A181487
%Y A364860 Cf. A000396, A002025, A002046, A118372, A364858, A364859.
%K A364860 nonn,more
%O A364860 1,1
%A A364860 _Amiram Eldar_, Aug 11 2023