A234498 Products p*q*r*s of distinct primes for which (p*q*r*s - 1)/2 is prime.

1155, 1995, 3135, 3255, 3315, 4935, 5115, 5187, 6783, 7035, 7095, 7215, 7395, 7455, 7755, 8463, 8547, 8715, 9867, 10335, 10455, 10695, 10815, 11055, 11715, 11739, 12243, 12903, 14595, 14835, 15855, 16107, 16359, 16779, 16863, 17043, 17255, 17355, 18183

Offset

1,1

Links

Table of n, a(n) for n=1..39.

Example

1155 = 3*5*7*11 is the least product of 4 distinct primes p,q,r,s for which (p*q*r*s-1)/2 is a prime: 577.

Mathematica

t = Select[Range[1, 20000, 2], Map[Last, FactorInteger[#]] == Table[1, {4}] &]; Take[(t - 1)/2, 120] (* A234105 *)
v = Flatten[Position[PrimeQ[(t - 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}]  (* A234498 *)
(w - 1)/2 (* A234499 *) (* Peter J. C. Moses, Dec 23 2013 *)

Crossrefs

Cf. A234105, A234499, A234500, A234097.

Sequence in context: A309413 A378717 A046390 * A147577 A211133 A088012

Adjacent sequences: A234495 A234496 A234497 * A234499 A234500 A234501

Keyword

nonn,easy

Author

Clark Kimberling, Jan 01 2014

Status

approved