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A118696 Semiprimes which are divisible by their multiplicative digital root. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..48.

EXAMPLE

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.

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A001358.

Sequence in context: A087718 A033476 A183978 * A065856 A136357 A136356

Adjacent sequences:  A118693 A118694 A118695 * A118697 A118698 A118699

KEYWORD

base,nonn

AUTHOR

Luc Stevens (lms022(AT)yahoo.com), May 20 2006

EXTENSIONS

Corrected by R. J. Mathar, May 23 2006

More terms from Robert G. Wilson v, Aug 04 2006

STATUS

approved

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Last modified February 19 00:35 EST 2020. Contains 332028 sequences. (Running on oeis4.)