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A113525 Semiprimes in third spoke of a hexagonal spiral (A056107). 1
4, 49, 301, 589, 973, 2353, 2701, 3073, 4333, 5293, 5809, 6349, 6913, 7501, 8749, 9409, 10801, 11533, 13069, 14701, 15553, 16429, 23233, 24301, 25393, 27649, 30001 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

a(1) = 4 because A056107(1) = 3*1^2 + 1 = 4 = 2^2 is semiprime. A056107(2) = 3*2^2 + 1 = 13 is not in the sequence, as it is a prime. A056107(3) = 3*3^2 + 1 = 28 = 2^2 * 7 is not in the sequence, as it is a 3-almost prime. a(16) = 9409 because A056107(56) = 3*56^2 + 1 = 9409 = 97^2 is semiprime. a(27) = 30001 because A056107(100) = 3*100^2 + 1 = 30001 = 19 * 1579 is semiprime.

FORMULA

{a(n)} = {3*n^2 + 1 iff semiprime}. {a(n)} = A056107 INTERSECT A001358.

CROSSREFS

Cf. A001358, A056107.

Sequence in context: A100256 A163944 A000596 * A064751 A045787 A067474

Adjacent sequences:  A113522 A113523 A113524 * A113526 A113527 A113528

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post (jvospost3(AT)gmail.com), Jan 12 2006

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Last modified February 15 08:12 EST 2012. Contains 205724 sequences.