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A158526
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n and (1 + 2*n + 2*n^2) are primes.
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1
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| Numbers n such that A048395(n) is semiprime, or A048395(n)/n is prime.
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LINKS
| Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
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EXAMPLE
| A048395(2)=26=2*13, A048395(5)=305=5*61, A048395(7)=791=7*113.
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MATHEMATICA
| f[n_]:=PrimeQ[n^2+(n+1)^2]; lst={}; Do[p=Prime[n]; If[f[p], AppendTo[lst, p]], {n, 6!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 27 2009]
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PROG
| (PARI) forprime(p=2, 1e4, if(isprime(2*p*(p+1)+1), print1(p", ")))
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CROSSREFS
| Cf. A048395 Sum of consecutive nonsquares, A001358 Semiprimes : products of two primes.
Sequence in context: A038875 A019334 A045356 * A146364 A105895 A023517
Adjacent sequences: A158523 A158524 A158525 * A158527 A158528 A158529
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KEYWORD
| nonn,easy
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Mar 20 2009
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EXTENSIONS
| Program and b-file by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Sep 09 2009
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