A118698 Smaller of two consecutive semiprimes with the same multiplicative digital root.

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

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: A044027 A020175 A374011 * A350203 A103381 A101577

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