A342644 Primes in A340180.

2, 2, 7, 23, 19, 43, 137, 139, 239, 283, 373, 491, 1019, 929, 2609, 2699, 1499, 4451, 3191, 4441, 5261, 3251, 6373, 7853, 8623, 9013, 6359, 10289, 9109, 6833, 7703, 13417, 19441, 15329, 19793, 9311, 16319, 13109, 12539, 23899, 26347, 10111, 11351, 19687, 27851, 13627, 34129, 18521, 27277, 35537

Offset

1,1

Comments

Terms are listed in the order in which they appear in A340180, including repetitions.

Repeated terms include a(1) = a(2) = 2, a(55) = a(56) = 17333, and a(233) = a(319) = 1253761. Are there any others?

Links

Robert Israel, Table of n, a(n) for n = 1..5000

Formula

a(n) = A340180(A342630(n)).

Example

a(4) = A340180(A342630(4)) = A340180(14) = 23.

Maple

f:= proc(n) local s, k;
  s:= numtheory:-sigma(n);
  add(`if`(igcd(n, k)=1, s mod k, 0), k=1..n-1);
end proc:
select(isprime, map(f, [$1..1000]));

Mathematica

Select[Array[Sum[Mod[DivisorSigma[1, #], k] Floor[1/GCD[k, #]], {k, # - 1}] &, 500], PrimeQ] (* Michael De Vlieger, Mar 17 2021 *)

Crossrefs

Cf. A340180, A342630.

Sequence in context: A156520 A307426 A343577 * A069101 A221648 A138802

Adjacent sequences: A342641 A342642 A342643 * A342645 A342646 A342647

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Mar 17 2021

Status

approved