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 A191915 Semiprimes p*q with p < q such that the concatenation p||q is again a product of two distinct primes. 2
 15, 26, 34, 35, 38, 55, 57, 69, 74, 85, 87, 91, 94, 95, 106, 118, 119, 123, 134, 161, 185, 202, 206, 209, 213, 215, 217, 221, 254, 259, 265, 295, 298, 303, 309, 314, 321, 334, 339, 346, 362, 365, 371, 377, 381, 382, 393, 395, 398, 407, 415, 417, 437, 445 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A subsequence of A191913 and of A191911. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 MATHEMATICA okQ[n_]:=Module[{fd=FromDigits[Flatten[IntegerDigits/@ Transpose[ FactorInteger[ n]][[1]]]]}, PrimeOmega[fd]==PrimeNu[fd]==2]; With[ {sps = Select[Range[500], PrimeOmega[#] == PrimeNu[#] == 2 &]}, Select[ sps, okQ]] (* From Harvey P. Dale, Nov 22 2011 *) PROG (PARI) for(i=1, 500, is_A006881(i)|next; f=factor(i); is_A006881(eval(Str(f[1, 1], f[2, 1]))) & print1(i", ")) CROSSREFS Sequence in context: A146249 A074974 A191913 * A189045 A032609 A050699 Adjacent sequences:  A191912 A191913 A191914 * A191916 A191917 A191918 KEYWORD nonn,base AUTHOR M. F. Hasler, Jun 19 2011 STATUS approved

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Last modified May 21 06:39 EDT 2013. Contains 225476 sequences.