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Search: id:A118694
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| A118694 |
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Semiprimes which are divisible by the product of their digits. |
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+0
2
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| 4, 6, 9, 15, 111, 115, 1111, 1115, 11111, 1111111, 1111117, 111111115
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The Mathematica coding is only good for multidigital non repunits numbers. Obviously 4,6&9 are members and so are A102782: Repunit semiprimes. - Robert G. Wilson v Jun 10 2006.
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FORMULA
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a(n)=A001358(k): A007954(a(n)) | a(n) - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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EXAMPLE
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115 is in the sequence because (1) it is a semiprime, (2) the product of its digits is 1*1*5=5 and (3) 115 is divisible by 5.
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MATHEMATICA
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lst = {}; Do[ p = Times @@ IntegerDigits@n; If[ PrimeQ@p && PrimeQ[n/p], AppendTo[lst, n]; Print[n]], {n, 275*10^6}]; lst - Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 10 2006
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PROGRAM
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(PARI) A007954(n)= { local(resul, ncpy); if(n<10, return(n) ); ncpy=n; resul = ncpy % 10; ncpy = (ncpy - ncpy%10)/10; while( ncpy > 0, resul *= ncpy %10; ncpy = (ncpy - ncpy%10)/10; ); return(resul); } { for(n=4, 50000000, if( bigomega(n)==2, dr=A007954(n); if(dr !=0 && n % dr == 0, print1(n, ", "); ); ); ); } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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CROSSREFS
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Cf. A001358, A102782, A046413, A118693.
Sequence in context: A136356 A136358 A115665 this_sequence A085648 A045114 A010436
Adjacent sequences: A118691 A118692 A118693 this_sequence A118695 A118696 A118697
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KEYWORD
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base,more,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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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
a(12) from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 10 2006
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