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 A122492 Semiprimes k such that 1 + 2k + 3k^2 is also semiprime. 1
 4, 6, 9, 10, 15, 21, 22, 33, 35, 57, 69, 77, 82, 86, 95, 111, 123, 134, 143, 146, 161, 183, 202, 203, 209, 218, 219, 221, 249, 262, 267, 298, 299, 302, 314, 321, 323, 326, 329, 334, 335, 339, 341, 417, 422, 446, 454, 471, 489, 515, 543, 551, 554, 562, 566, 573 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..3500 EXAMPLE k = 4 = 2*2 (semiprime) is a term because 1 + 2k + 3k^2 = 57 = 3*19 (semiprime), etc. MATHEMATICA Select[Range[600], PrimeOmega[#]==PrimeOmega[1+2#+3#^2]==2&] (* Harvey P. Dale, Nov 04 2023 *) PROG (Magma) IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [2..600] | IsSemiprime(n) and IsSemiprime(1+2*n+3*n^2)]; // Vincenzo Librandi, Jan 09 2019 CROSSREFS Cf. A086285 (numbers k such that 1 + 2k + 3k^2 is prime). Sequence in context: A137167 A181564 A119961 * A178378 A133234 A111206 Adjacent sequences: A122489 A122490 A122491 * A122493 A122494 A122495 KEYWORD nonn AUTHOR Zak Seidov, Oct 20 2006 STATUS approved

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Last modified September 14 06:54 EDT 2024. Contains 375920 sequences. (Running on oeis4.)