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A109837
Smallest prime factor of the reverse concatenation of the first n odd numbers.
4
31, 3, 17, 7, 3, 1579, 17, 3, 2677, 131, 3, 54049423, 47, 3, 487, 25541, 3, 7, 211, 3, 31, 622639, 3, 498508631, 7, 3, 1259, 193, 3, 7669, 16229, 3, 13, 887377, 3, 737169676563615957555351494745434139373533312927252321191715131197531
OFFSET
2,1
COMMENTS
Sequence starts with offset 2 since A038395(1)=1 has no prime factor. - M. F. Hasler
Starting with 2nd term each 3rd term is a(3m)=3.
Sequence A089922={3,73,123,817,...} lists the largest odd number (2n-1) used in the terms a(n) which are primes or probable primes.
LINKS
FORMULA
a(n) = A020639(A038395(n)). - R. J. Mathar, Sep 16 2007
EXAMPLE
n=6: a(6)=1579 because 131197531=1579*83089.
MATHEMATICA
s=1; Do[news=FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[s]}]]; fi=FactorInteger[news][[1, 1]]; Print[fi]; s=news, {n, 3, 70, 2}]
PROG
(PARI) t=1; for( n=2, 99, print1( factor( eval( t=Str( 2*n-1, t)))[1, 1], ", ")) \\ M. F. Hasler, Apr 13 2008
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Zak Seidov, Jul 04 2005
EXTENSIONS
More terms from R. J. Mathar, Sep 16 2007
Edited by M. F. Hasler, Apr 14 2008
Edited by T. D. Noe, Oct 30 2008
STATUS
approved