A156165 Numbers k such that k![7]+1 is prime (n![7] = A114799(n) = septuple factorial).

0, 1, 2, 4, 6, 9, 10, 12, 13, 24, 25, 26, 29, 31, 35, 36, 47, 49, 57, 58, 64, 71, 73, 75, 78, 80, 97, 123, 125, 129, 131, 135, 147, 150, 159, 183, 201, 250, 251, 255, 298, 336, 337, 458, 467, 556, 570, 657, 743, 801, 908, 925, 1003, 1209, 1473, 1524, 1716, 1881, 1926

Offset

1,3

Comments

a(103) > 50000. - Robert Price, Sep 03 2012

Links

Robert Price, Table of n, a(n) for n = 1..102

C. Caldwell and H. Dubner (Eds): The top ten prime numbers: from the unpublished collections of R. Ondrejka (May 2001), Table 21 F, p. 75

Ken Davis, Status of Search for Multifactorial Primes.

Ken Davis, Results for n!7+1.

Mathematica

mf[n_, k_] := Product[n - i k, {i, 0, Quotient[n - 2, k]}];
Reap[For[k = 0, k <= 2000, k++, If[PrimeQ[mf[k, 7] + 1], Sow[k]]]][[2, 1]] (* Jean-François Alcover, Feb 26 2019 *)
Select[Range[0, 2000], PrimeQ[Times@@Range[#, 1, -7]+1]&] (* Harvey P. Dale, Aug 21 2021 *)

Prog

(PARI) mf(n, k=7)=prod(i=0, (n-2)\k, n-i*k)
for( n=0, 9999, ispseudoprime(mf(n)+1) & print1(n", "))

Crossrefs

Cf. A156167, A085150, A085148, A085146, A037083, A080778, A002981.

Sequence in context: A210380 A228359 A347745 * A024968 A047411 A368342

Adjacent sequences: A156162 A156163 A156164 * A156166 A156167 A156168

Keyword

nonn

Author

M. F. Hasler, Feb 10 2009

Status

approved