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A207526 Primes p such that p-2 or p+2 are semiprimes. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

EXAMPLE

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)

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}) &]

CROSSREFS

Cf. A063637, A063638, A063643.

Sequence in context: A173135 A020627 A043292 * A175442 A020597 A140563

Adjacent sequences:  A207523 A207524 A207525 * A207527 A207528 A207529

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Feb 18 2012

STATUS

approved

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Last modified January 27 13:23 EST 2022. Contains 350607 sequences. (Running on oeis4.)