A340741 Numbers k such that A340740(k) is prime.

7, 8, 9, 11, 12, 13, 15, 18, 19, 28, 31, 32, 34, 36, 44, 46, 47, 51, 52, 62, 64, 67, 69, 70, 73, 83, 88, 109, 110, 112, 128, 148, 153, 159, 189, 190, 192, 206, 212, 214, 222, 224, 226, 244, 245, 261, 267, 269, 280, 282, 283, 287, 300, 305, 312, 315, 319, 323, 366, 370, 378, 381, 388, 394, 404

Offset

1,1

Links

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

Example

a(3) = 9 is a term because A340740(9) = 2 is prime.

Maple

f:= proc(n) local k;
  add(`if`(igcd(k, n)=1, n mod k, 0), k=1..floor(n/2))
end proc:
select(t -> isprime(f(t)), [$1..1000]);

Mathematica

A340741[n_] :=
  Position[Table[
     PrimeQ[Sum[
       Mod[m, i]*Floor[1/GCD[i, m]], {i, Floor[(m - 1)/2]}]], {m, 1,
      n}], True] // Flatten;
A340741[404] (* Robert P. P. McKone, Jan 19 2021 *)

Prog

(PARI) isok(n) = isprime(sum(k=1, n\2, if (gcd(k, n)==1, n%k))); \\ Michel Marcus, Jan 18 2021

Crossrefs

Cf. A340731, A340740, A340742.

Sequence in context: A035705 A205698 A210147 * A097338 A196040 A196043

Adjacent sequences: A340738 A340739 A340740 * A340742 A340743 A340744

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Jan 18 2021

Status

approved