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Search: id:A118688
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| A118688 |
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Semiprimes for which the sum of the digits is also a semiprime. |
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+0
1
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| 4, 6, 9, 15, 22, 33, 46, 51, 55, 69, 77, 82, 86, 87, 91, 95, 118, 121, 123, 141, 145, 158, 159, 177, 185, 194, 202, 213, 217, 226, 235, 249, 253, 262, 267, 301, 303, 321, 329, 334, 339, 361, 365, 393, 411, 415, 437, 446, 447, 451, 473, 482, 489, 501, 505, 514
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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55 is in the sequence because (1) it is a semiprime and (2) the sum of its digits 5+5=10 is also a semiprime.
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PROGRAM
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(PARI) A007953(n)= { local(resul); resul=0; while(n>0, resul += n%10; n = (n-n%10)/10; ); return(resul); } { for(n=4, 600, if( bigomega(n)==2, if(bigomega(A007953(n)) == 2, print1(n, ", "); ); ); ); } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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CROSSREFS
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Cf. A001358.
Sequence in context: A078443 A085751 A116589 this_sequence A118691 A087718 A033476
Adjacent sequences: A118685 A118686 A118687 this_sequence A118689 A118690 A118691
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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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EXTENSIONS
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Corrected by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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