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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
OFFSET
1,1
LINKS
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
KEYWORD
base,nonn
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), May 20 2006
EXTENSIONS
Corrected by R. J. Mathar, May 23 2006
STATUS
approved