A351872 Numbers k such that either k-1 or k/2 is prime, but not both.

3, 8, 10, 12, 18, 20, 22, 24, 26, 30, 32, 34, 42, 44, 46, 48, 54, 58, 60, 68, 72, 80, 82, 84, 86, 90, 94, 98, 102, 104, 106, 108, 110, 114, 118, 122, 128, 132, 134, 138, 140, 142, 146, 150, 152, 164, 166, 168, 174, 178, 180, 182, 192, 198, 200, 202, 206, 212, 214, 218, 224, 226

Offset

1,1

Comments

Numbers k with exactly 1 divisor d such that k-d is prime.

Links

Table of n, a(n) for n=1..62.

Mathematica

Select[Range[250], Xor @@ PrimeQ[{#-1, #/2}] &] (* Amiram Eldar, Feb 23 2022 *)
Select[Range[250], Total[Boole[PrimeQ[{#-1, #/2}]]]==1&] (* Harvey P. Dale, Nov 05 2023 *)

Prog

(PARI) isok(k) = bitxor(isprime(k-1), !(k%2) && isprime(k/2)); \\ Michel Marcus, Feb 23 2022

Crossrefs

Cf. A351863.

Sequence in context: A327308 A350667 A287371 * A226641 A212966 A074186

Adjacent sequences: A351869 A351870 A351871 * A351873 A351874 A351875

Keyword

nonn

Author

Wesley Ivan Hurt, Feb 22 2022

Status

approved