A323331 Smallest member of sociable quadruples using Dedekind psi function (A001615).

11398670, 22797340, 38369450, 45594680, 56993350, 59334310, 76738900, 91189360, 113986700, 118668620, 153477800, 182378720, 209524210, 227973400, 237337240, 268586150, 284966750, 306955600, 364757440, 419048420, 455946800, 474674480, 537172300, 539867650, 569933500

Offset

1,1

Comments

Numbers k whose iterations of k -> A001615(k) - k are cyclic with a period of 4, and in each cyclic quadruple k is the least of the 4 members.

Links

Table of n, a(n) for n=1..25.

Example

11398670 is in the sequence since the iterations of k -> A001615(k) - k are cyclic with a period of 4: 11398670, 11475730, 12474350, 14093650, 11398670, ... and 11398670 is the smallest member of the quadruple.

Mathematica

t[0]=0; t[1]=0; t[n_]:=(Times@@(1+1/Transpose[FactorInteger[n]][[1]])-1)*n;
seq[n_]:=NestList [t, n, 4][[2;; 5]] ; aQ[n_] := Module[ {s=seq[n]}, n==Min[s] && Count[s, n]==1]; s={}; Do[If[aQ[n], AppendTo[s, n]], {n, 1, 10^9}]; s

Crossrefs

Cf. A001615, A090615, A319902, A319915, A323327, A323328, A323329, A323330.

Sequence in context: A069341 A204790 A183826 * A072142 A043674 A141281

Adjacent sequences: A323328 A323329 A323330 * A323332 A323333 A323334

Keyword

nonn

Author

Amiram Eldar, Jan 11 2019

Status

approved