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A340741 Numbers k such that A340740(k) is prime. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 24 17:23 EDT 2022. Contains 354042 sequences. (Running on oeis4.)