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
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
Programs
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Mathematica
Select[4*Range[0, 300] + 3, PrimeQ[#] && ! PrimeQ[(# + 3)/2] &] (* Amiram Eldar, Oct 18 2021 *)
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PARI
isA348421(n) = isprime(n) && (n%4==3) && !isprime((n+3)/2)
Formula
a(n) = 2*A348423(n) - 3.
Comments