A218172 Centered 12-gonal numbers which are semiprimes, intersection of A003154 and A001358.

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

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