A392871 Numbers k such that k == 1 mod A117366(k), where A117366(n) gives the smallest prime greater than the largest prime dividing n.

1, 4, 6, 15, 16, 36, 50, 52, 56, 64, 66, 81, 96, 120, 153, 186, 210, 216, 225, 256, 273, 323, 352, 370, 400, 435, 441, 476, 486, 495, 540, 552, 576, 671, 672, 715, 750, 760, 861, 924, 936, 949, 960, 980, 1017, 1024, 1068, 1122, 1134, 1197, 1210, 1296, 1334, 1445, 1505, 1536, 1750, 1768, 1770, 1782, 1800, 1820, 1887

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Example

15 = 3*5, the next larger prime is 7, so 15 mod 7 = 1, and therefore 15 is included as a term.

Mathematica

a117336[n_]:=NextPrime[FactorInteger[n][[-1, 1]]]; okQ[k_]:=Mod[k, a117336[k]]==1; Select[Range[1887], okQ] (* James C. McMahon, Jan 27 2026 *)

Prog

(PARI)
A006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1);
A392865(n) = (n%nextprime(1+A006530(n)));
is_A392871(k) = (1==A392865(k));

Crossrefs

Positions of 1's in A392865 and in A392870.

Cf. A117366.

Sequence in context: A048753 A055719 A349157 * A117883 A106387 A034771

Adjacent sequences: A392868 A392869 A392870 * A392872 A392873 A392874

Keyword

nonn

Author

Antti Karttunen, Jan 27 2026

Status

approved