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A226993 Primes p such that 2p - 1 and 2p + 1 are squarefree. 3
2, 3, 7, 11, 17, 19, 29, 43, 47, 53, 71, 79, 83, 89, 97, 101, 107, 109, 127, 151, 173, 179, 191, 197, 199, 223, 227, 233, 241, 251, 271, 277, 281, 307, 317, 331, 349, 353, 359, 379, 389, 397, 431, 439, 443, 449, 457, 461, 467, 479, 503, 521, 523, 547, 557, 569 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..1000

EXAMPLE

3 is in the sequence because 3 is prime and both 2*3 - 1 = 5 and 2*3 + 1 = 7 are squarefree.

MAPLE

with(numtheory); P:=proc(q) local n; for n from 1 to q do

if isprime(n) then if issqrfree(2*n-1) and issqrfree(2*n+1) then print(n)

fi; fi; od; end: P(10^5); #Paolo P. Lava, Jun 26 2013

PROG

(PARI) is(n)=isprime(n)&&issquarefree(2*n-1)&&issquarefree(2*n+1) \\ Charles R Greathouse IV, Jun 27 2013

CROSSREFS

Cf. A005117.

Sequence in context: A040103 A045323 A161185 * A235482 A155141 A127944

Adjacent sequences:  A226990 A226991 A226992 * A226994 A226995 A226996

KEYWORD

nonn

AUTHOR

Irina Gerasimova, Jun 26 2013

STATUS

approved

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Last modified September 30 05:03 EDT 2020. Contains 337435 sequences. (Running on oeis4.)