OFFSET
2,1
COMMENTS
If 10 doen't divide n, number of digits of n is l and both numbers n & reversal(n) have the same sum of prime factors then for all positive numbers k, n*(10^(k*l)-1)/(10^l-1) has the same property (See the mentioned link).
LINKS
Carlos Rivera SOPF(N)=SOP(RN)
EXAMPLE
250 = 2*5*5*5, reversal(250) = 2*2*13, sum of the prime factors of both these are equal, namely 17 and since 250 is the smallest 3-digit number with this property, so
a(3) = 250.
MATHEMATICA
r[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; sop[n_]:=(b=FactorInteger[n]; l=Length[b]; Sum[b[[k]][[1]]*b[[k]][[2]], {k, l}]); a[n_]:=(For[k=1, 10^(n-1)+kŠr[10^(n-1)+k]||sop[10^(n-1)+k]¹sop[r[10^(n-1)+k]], k++]; 10^(n-1)+k)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. M. Bergot & Farideh Firoozbakht, Dec 24 2010
STATUS
approved