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 A109837 Smallest prime factor of the reverse concatenation of the first n odd numbers. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A038395, A089922, A104644, A138965. Sequence in context: A040949 A050101 A107811 * A128372 A040942 A153072 Adjacent sequences:  A109834 A109835 A109836 * A109838 A109839 A109840 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

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Last modified March 22 04:32 EDT 2019. Contains 321406 sequences. (Running on oeis4.)