cp's OEIS Frontend

A364859 Lesser of a pair of S-amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A364858(k).

%I A364859 #9 Aug 12 2023 02:29:04
%S A364859 186,1184,2030,6232,10744,66928,522405,643336,5459176,7677248,
%T A364859 13223490,16137628,25596544,26090325,28118032,31772524,34364912,
%U A364859 40504324,133178325
%N A364859 Lesser of a pair of S-amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A364858(k).
%C A364859 S-amicable numbers are analogous to amicable numbers (A002025/A002046) as S-perfect numbers (A118372) are analogous to perfect numbers (A000396).
%C A364859 The greater counterparts are in A364860.
%F A364859 a(n) = A364858(A364860(n)).
%e A364859 186 is a term since A364858(186) = 198 > 186, and A364858(198) = 186.
%t A364859 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, sum]]]], {n, 2, nmax}]; am]; seq[10^4]
%o A364859 (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(s,", "))));} \\ after _M. F. Hasler_ at A181487
%Y A364859 Cf. A000396, A002025, A002046, A118372, A364858, A364860.
%K A364859 nonn,more
%O A364859 1,1
%A A364859 _Amiram Eldar_, Aug 11 2023