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Search: id:A118689
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| A118689 |
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Semiprimes for which the product of the digits is also a semiprime. |
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+0
1
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| 4, 6, 9, 14, 22, 25, 33, 35, 55, 57, 77, 91, 119, 122, 123, 133, 141, 155, 161, 177, 213, 215, 217, 221, 321, 371, 411, 515, 517, 551, 611, 713, 717, 721, 731, 771, 1114, 1119, 1133, 1135, 1137, 1141, 1157, 1177, 1191, 1271, 1313, 1315, 1317, 1351, 1371, 1411
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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77 is in the sequence because (1 )it is a semiprime and (2) the product of its digits 7*7=49 is also a semiprime.
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PROGRAM
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(PARI) A007954(n)= { local(resul) ; if(n==0, return(0) ; ) ; resul= 1 ; while(n>0, resul *= n%10 ; n = (n-n%10)/10 ; ) ; return(resul) ; } { for(n=4, 2000, if( bigomega(n)==2, if(A007954(n) != 0 && bigomega(A007954(n)) == 2, print1(n, ", "); ) ; ) ; ) ; } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 21 2006
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CROSSREFS
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Cf. A001358.
Sequence in context: A094750 A057988 A073679 this_sequence A118692 A020706 A137371
Adjacent sequences: A118686 A118687 A118688 this_sequence A118690 A118691 A118692
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), May 20 2006
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