

A113548


Least nonpalindromic number k such that k and its digital reversal both have exactly n prime divisors.


1




OFFSET

1,1


LINKS

Table of n, a(n) for n=1..10.


EXAMPLE

a(1)=13=13 since 31=31,
a(2)=12=2^2*3 since 21=3*7
a(3)=132=2^2*3*11 since 231=3*7*11
...
a(7)=10444434=2*3*7*11*13*37*47 since 43444401=3*7*11*13*17*23*37
a(8)=241879638=2*3*7*11*13*17*23*103 since 836978142=2*3*7*11*13*23*73*83


MATHEMATICA

r[n_] := FromDigits[ Reverse[ IntegerDigits[ n]]]; f[n_] := Block[{k = r[n], len = Length[ FactorInteger[n]]}, If[k != n && len == Length[ FactorInteger[ r[n]]], len, 0]]; t = Table[0, {10}]; Do[ a = f[n]; If[a > 0 && t[[a]] == 0, t[[a]] = n; Print[{a, n}]], {n, 107}]; t


CROSSREFS

Cf. A110843, A110819.
Sequence in context: A212526 A019331 A004454 * A249998 A195210 A175850
Adjacent sequences: A113545 A113546 A113547 * A113549 A113550 A113551


KEYWORD

base,hard,nonn


AUTHOR

Ryan Propper and Robert G. Wilson v, Sep 21 2005


EXTENSIONS

Edited and extended by Giovanni Resta, Jan 16 2006
a(9)a(10) from Giovanni Resta, Feb 23 2014


STATUS

approved



