A364860 - OEIS

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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).

198, 1210, 2220, 6368, 10856, 66992, 525915, 652664, 5495264, 7684672, 13727466, 16150628, 25640096, 26138475, 28128368, 33642028, 34380688, 40803868, 133471275

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OFFSET

1,1

COMMENTS

S-amicable numbers are analogous to amicable numbers (A002025/A002046) as S-perfect numbers (A118372) are analogous to perfect numbers (A000396).

The terms are ordered according to their lesser counterparts (A364859).

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(n) = A364858(A364859(n)).

EXAMPLE

198 is a term since A364858(198) = 186 < 198, and A364858(186) = 198.

MATHEMATICA

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]

PROG

(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

CROSSREFS

Cf. A000396, A002025, A002046, A118372, A364858, A364859.

Sequence in context: A065697 A159204 A075457 * A224452 A227705 A331098

Adjacent sequences: A364857 A364858 A364859 * A364861 A364862 A364863

KEYWORD

nonn,more

AUTHOR

Amiram Eldar, Aug 11 2023

STATUS

approved