A348421 Primes p == 3 (mod 4) such that (p+3)/2 is not prime.

47, 67, 107, 127, 151, 167, 179, 227, 239, 263, 283, 307, 347, 367, 431, 439, 467, 487, 491, 503, 547, 571, 587, 599, 607, 643, 647, 683, 719, 727, 739, 751, 787, 811, 823, 827, 887, 907, 947, 967, 983, 991, 1019, 1031, 1051, 1063, 1087, 1103, 1163, 1187

Offset: 1

Author

Jianing Song, Oct 18 2021

Keywords

• nonn
• easy

Comments

Complement of A092109 with respect to A002145.

Examples

			47 is a term since it is a prime congruent to 3 modulo 4 and (47+3)/2 = 25 is composite.
		

Links

• Jianing Song, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002145, A092109, A348423.

Programs

Mathematica

Select[4*Range[0, 300] + 3, PrimeQ[#] && ! PrimeQ[(# + 3)/2] &] (* Amiram Eldar, Oct 18 2021 *)

PARI

isA348421(n) = isprime(n) && (n%4==3) && !isprime((n+3)/2)

Formula

a(n) = 2*A348423(n) - 3.