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A324255 Lesser of super amicable pair m < n defined by sigma(sigma(m)) = sigma(sigma(n)) = m + n. 1
23, 14999, 34673, 55373, 2056961, 2458187, 4586987, 5174363, 6204767, 15788453, 20699927, 22239647, 25748273, 43428947, 53636627, 74005637, 92626307, 132253139, 134131379, 158486747, 167677187, 183614987, 307412933, 385042487, 413859143, 418168343, 683772017 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The larger numbers in each pair are in A324256.

Analogous to A002025 as A019279 is analogous to A000396.

LINKS

Table of n, a(n) for n=1..27.

EXAMPLE

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

MATHEMATICA

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

PROG

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

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

CROSSREFS

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

Sequence in context: A090674 A013728 A028693 * A273940 A348307 A033998

Adjacent sequences:  A324252 A324253 A324254 * A324256 A324257 A324258

KEYWORD

nonn

AUTHOR

Amiram Eldar, Feb 19 2019

STATUS

approved

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Last modified December 3 20:35 EST 2021. Contains 349468 sequences. (Running on oeis4.)