A252090 Primes p such that p + 28 is also prime.

3, 13, 19, 31, 43, 61, 73, 79, 103, 109, 139, 151, 163, 199, 211, 223, 229, 241, 283, 331, 373, 421, 433, 439, 463, 541, 571, 613, 619, 631, 673, 691, 733, 769, 811, 829, 853, 859, 883, 919, 991, 1021, 1033, 1063, 1069, 1123, 1153, 1201, 1231, 1249

Offset: 1

Author

Vincenzo Librandi, Dec 14 2014

Keywords

• nonn
• easy

Examples

			19 is in the sequence because 19 is prime and 19 + 28 = 47 is also prime.
433 is in the sequence because 433 is prime and 433 + 28 = 461 is also prime.
		

Links

• Karl V. Keller, Jr., Table of n, a(n) for n = 1..10000

Programs

Magma

[NthPrime(n): n in [1..250] | IsPrime(NthPrime(n)+28)];

Maple

P:= select(isprime, {seq(2*i+1, i=1..10000)}):
P intersect map(`-`,P,28);
# if using Maple 11 or earlier, uncomment the next line
# sort(convert(%,list));  # Robert Israel, Dec 14 2014

Mathematica

Select[Prime[Range[250]], PrimeQ[# + 28] &]

PARI

is(n)=isprime(n)&&isprime(n+28) \\ Anders Hellström, Dec 01 2015