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A158526 n and (1 + 2*n + 2*n^2) are primes. 2
2, 5, 7, 17, 19, 29, 47, 79, 97, 109, 137, 139, 149, 157, 167, 199, 229, 347, 349, 389, 409, 467, 479, 547, 577, 599, 709, 719, 757, 857, 929, 937, 967, 1039, 1069, 1087, 1187, 1229, 1259, 1399, 1409, 1447, 1559, 1579, 1597, 1607, 1657, 1697, 1699, 1709 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that A048395(n) is semiprime, or A048395(n)/n is prime.

Or, primes in A027861. Also, (1+2*n+2*n^2) are in A027862. - Zak Seidov, Sep 19 2015

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

A048395(2)=26=2*13, A048395(5)=305=5*61, A048395(7)=791=7*113.

MATHEMATICA

f[n_]:=PrimeQ[n^2+(n+1)^2]; lst={}; Do[p=Prime[n]; If[f[p], AppendTo[lst, p]], {n, 6!}]; lst (* Vladimir Joseph Stephan Orlovsky, Oct 27 2009 *)

PROG

(PARI) forprime(p=2, 1e4, if(isprime(2*p*(p+1)+1), print1(p", "))) \\ Charles R Greathouse IV, Sep 09 2009

(MAGMA) [p: p in PrimesUpTo(2000) | IsPrime(2*p^2+2*p+1)]; // Vincenzo Librandi, Jun 22 2014

CROSSREFS

Cf. A048395 (sum of consecutive nonsquares), A001358 (semiprimes).

Cf. A027861, A027862.

Sequence in context: A038875 A019334 A045356 * A146364 A105895 A238699

Adjacent sequences:  A158523 A158524 A158525 * A158527 A158528 A158529

KEYWORD

nonn,easy

AUTHOR

Zak Seidov, Mar 20 2009

STATUS

approved

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Last modified April 20 17:54 EDT 2019. Contains 322310 sequences. (Running on oeis4.)