OFFSET
1,1
COMMENTS
Integers with digital root 3, 6 or 9 are divisible by 3, so 3 is the only palindromic prime with digital root 3 and there are no palindromic primes with digital root 6 or 9.
LINKS
Shyam Sunder Gupta, Table of n, a(n) for n = 1..5953
FORMULA
EXAMPLE
a(7)=5 because the 7th palindromic prime is 131 and 1+3+1 = 5.
MATHEMATICA
t = {}; Do[z = n*10^(IntegerLength[n] - 1) + FromDigits@Rest@Reverse@IntegerDigits[n]; If[PrimeQ[z], AppendTo[t, Mod[z, 9]]], {n, 1, 99999}]; Insert[t, 2, 5]
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
Shyam Sunder Gupta, Oct 02 2013
STATUS
approved