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A118696
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Semiprimes which are divisible by their multiplicative digital root.
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0
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4, 6, 9, 15, 26, 34, 35, 62, 111, 115, 134, 278, 314, 355, 395, 398, 535, 694, 755, 1111, 1115, 1126, 1135, 1315, 1322, 1355, 1535, 1795, 2962, 3155, 3338, 3662, 3898, 3994, 4174, 4714, 5315, 6166, 6326, 6334, 6362, 6686, 6866, 6914, 6922, 7115, 7195, 7915
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..48.
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EXAMPLE
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134 is in the sequence because (1)it is a semiprime, (2) the multiplicative digital root is 2 and (3) 134 is divisible by 2.
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MATHEMATICA
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spQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; mdrQ[n_] := Mod[n, NestWhile[Times @@ IntegerDigits@# &, n, UnsameQ, All]] == 0; Select[ Range@9754, spQ@# && mdrQ@# &] - Robert G. Wilson v, Aug 04 2006
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PROG
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(PARI) A031347(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(A031347(resul)); } { for(n=4, 5000, if( bigomega(n)==2, dr=A031347(n); if(dr !=0 && n % dr == 0, print1(n, ", "); ); ); ); } - R. J. Mathar, May 23 2006
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CROSSREFS
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Cf. A001358.
Sequence in context: A087718 A033476 A183978 * A065856 A136357 A136356
Adjacent sequences: A118693 A118694 A118695 * A118697 A118698 A118699
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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, May 23 2006
More terms from Robert G. Wilson v, Aug 04 2006
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STATUS
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approved
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