A207526 Primes p such that p-2 or p+2 are semiprimes.

2, 7, 11, 13, 17, 19, 23, 31, 37, 41, 47, 53, 59, 67, 71, 79, 83, 89, 97, 109, 113, 127, 131, 139, 157, 163, 167, 179, 181, 199, 211, 223, 233, 239, 251, 257, 263, 269, 293, 307, 311, 317, 331, 337, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 439

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Feb 18 2012

Keywords

• nonn

Examples

			2+2=2^2(semiprime), 7+2=3^2(semiprime), 11-2=3^2(semiprime), 13+2=3*5(semiprime), 17-2=3*5(semiprime)
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A063637, A063638, A063643.

Programs

Mathematica

Select[Table[Prime[n], {n,200}], (Last /@ FactorInteger[#-2] == {1,1} || Last /@ FactorInteger[#-2] == {2}) || (Last /@ FactorInteger[#+2] == {1,1} || Last /@ FactorInteger[#+2] == {2}) &]