

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
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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 (2n1) used in the terms a(n) which are primes or probable primes.


LINKS

Table of n, a(n) for n=2..37.


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*n1, 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



