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A118698 Smaller of two consecutive semiprimes with the same multiplicative digital root. 1
46, 65, 95, 155, 158, 185, 201, 202, 203, 205, 206, 253, 254, 278, 301, 302, 303, 305, 323, 326, 361, 382, 403, 417, 445, 451, 453, 454, 471, 473, 478, 493, 497, 501, 502, 514, 519, 526, 527, 529, 537, 538, 542, 543, 545, 554, 559, 562, 565, 566, 581, 583 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

46 and 49 are two consecutive semiprimes with the same multiplicative digital root, namely 8.

MATHEMATICA

mrt[{a_, b_}]:=NestWhile[Times@@IntegerDigits[#]&, a, #>9&]== NestWhile[ Times@@IntegerDigits[#]&, b, #>9&]; With[{semis=Partition[Select[Range[ 600], PrimeOmega[#]==2&], 2, 1]}, Transpose[Select[semis, mrt]][[1]]] (* Harvey P. Dale, Dec 17 2011 *)

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)); } { oldr=0; oldn=0; for(n=5, 1000, if( bigomega(n)==2, dr=A031347(n); if(dr==oldr, print1(oldn, ", "); ); oldr=dr; oldn=n; ); ); } - R. J. Mathar, May 23 2006

CROSSREFS

Cf. A001358.

Sequence in context: A043247 A044027 A020175 * A103381 A101577 A051413

Adjacent sequences:  A118695 A118696 A118697 * A118699 A118700 A118701

KEYWORD

base,nonn

AUTHOR

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

EXTENSIONS

Corrected by R. J. Mathar, May 23 2006

STATUS

approved

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Last modified May 28 03:04 EDT 2020. Contains 334671 sequences. (Running on oeis4.)