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

Author

Zak Seidov, Oct 22 2012

Keywords

• nonn

Comments

Might also be called 'semiprime star numbers'.

A083749 and A006061 are subsequences.

Examples

			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).
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A003154, A001358, A006061, A078972, A083749.

Programs

Mathematica

Select[Table[6n(n-1)+1,{n,100}],PrimeOmega[#]==2&] (* Harvey P. Dale, Sep 01 2014 *)

PARI

lista(nn) = {for (n = 1, nn, if (bigomega(v = 6*n*(n-1) + 1) == 2, print1(v, ", ")););} \\ Michel Marcus, Nov 09 2013