A204541 Semiprimes with semiprime "look and say" descriptions.

4, 14, 15, 21, 22, 35, 38, 55, 57, 74, 87, 95, 119, 143, 145, 166, 187, 205, 215, 217, 247, 253, 254, 259, 278, 287, 289, 291, 305, 314, 335, 339, 341, 394, 403, 407, 427, 471, 493, 505, 514, 515, 517, 538, 553, 559, 565, 589, 614, 622, 623, 629, 633, 634, 649

Offset: 1

Author

Robert G. Wilson v, Jan 27 2012

Keywords

• easy
• nonn

Comments

Semiprime analogous to A056815.

Examples

			14 is in the sequence because 14 is a semiprime (2*7) and its "Look and Say", 1114 is also a semiprime (2*557).
		

Crossrefs

Cf. A001358, A056815.

Programs

Mathematica

LookAndSayA[n_] := FromDigits@ Flatten@ IntegerDigits@ Flatten[ Through[ {Length, First}[#]] & /@ Split@ IntegerDigits@ n]; semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; Select[ Range@ 650, semiPrimeQ@# && semiPrimeQ@ LookAndSayA@# &]