A217707 Numbers k such that both 4*k-1 and 4*k+1 are composite.

14, 16, 19, 23, 29, 30, 31, 36, 40, 44, 46, 47, 51, 52, 54, 55, 59, 61, 62, 65, 72, 74, 75, 76, 80, 81, 82, 85, 86, 89, 91, 94, 98, 101, 103, 104, 106, 107, 109, 113, 118, 119, 121, 124, 128, 129, 132, 133, 134, 136, 138, 140, 145, 146, 149, 151, 156, 157, 159

Offset

1,1

Links

Table of n, a(n) for n=1..59.

Maple

q:= k-> not ormap(isprime, [4*k-1, 4*k+1]):
select(q, [$1..160])[];  # Alois P. Heinz, Apr 17 2026

Mathematica

Select[Range[200], ! PrimeQ[4 # - 1] && ! PrimeQ[4 # + 1] &]
(* Alternative: *)
Select[Range[200], AllTrue[4#+{1, -1}, CompositeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Aug 11 2015 *)

Prog

(PARI) isok(k) = (k>0) && !isprime(4*k-1) && !isprime(4*k+1); \\ Michel Marcus, Apr 17 2026

Crossrefs

Cf. A060461, A045751.

Sequence in context: A061365 A327822 A102107 * A176686 A007935 A076055

Adjacent sequences: A217704 A217705 A217706 * A217708 A217709 A217710

Keyword

nonn,easy

Author

Jayanta Basu, Mar 20 2013

Status

approved