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 A218172 Centered 12-gonal numbers which are semiprimes, intersection of A003154 and A001358. 2
 121, 253, 793, 1261, 1441, 1633, 1837, 2773, 3601, 3901, 4213, 4537, 4873, 5221, 7141, 9841, 11881, 14113, 14701, 16537, 17173, 17821, 19153, 19837, 21241, 22693, 23437, 24193, 24961, 28153, 28981, 29821, 30673, 34201, 37921, 38881, 39853, 40837, 41833, 43861, 45937, 48061, 49141, 50233, 53581, 55873 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Might also be called 'semiprime star numbers'. A083749 and A006061 are subsequences. LINKS Zak Seidov, Table of n, a(n) for n = 1..1000 EXAMPLE a(1) = 121 = 11^2 = A001358(40) = A003154(5) = A083749(1) = A006061(1) = A078972(11). a(2) = 253 = 11*23 = A001358(81) = A003154(7) = A083749(2) = A078972(18). MATHEMATICA Select[Table[6n(n-1)+1, {n, 100}], PrimeOmega[#]==2&] (* Harvey P. Dale, Sep 01 2014 *) PROG (PARI) lista(nn) = {for (n = 1, nn, if (bigomega(v = 6*n*(n-1) + 1) == 2, print1(v, ", ")); ); } \\ Michel Marcus, Nov 09 2013 CROSSREFS Cf. A003154, A001358, A006061, A078972, A083749. Sequence in context: A131973 A045571 A088285 * A083749 A211468 A023696 Adjacent sequences:  A218169 A218170 A218171 * A218173 A218174 A218175 KEYWORD nonn AUTHOR Zak Seidov, Oct 22 2012 STATUS approved

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Last modified January 20 20:50 EST 2021. Contains 340332 sequences. (Running on oeis4.)