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A229875
Iterated sum-of-digits of palindromic prime; or digital root of palindromic prime.
7
2, 3, 5, 7, 2, 2, 5, 7, 1, 2, 7, 2, 4, 5, 7, 1, 4, 5, 1, 2, 5, 7, 8, 7, 8, 1, 4, 5, 2, 7, 8, 4, 8, 7, 8, 5, 8, 1, 2, 2, 7, 1, 4, 5, 1, 2, 7, 8, 1, 4, 5, 8, 4, 4, 5, 8, 1, 4, 7, 8, 1, 5, 2, 5, 4, 7, 4, 5, 2, 8, 7, 1, 2, 1, 7, 2, 7, 2, 4, 8, 4, 2, 2, 2, 5, 4
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
FORMULA
a(n) = A010888(A002385(n)). - R. J. Mathar, Sep 09 2015
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
Sequence in context: A142711 A357096 A093338 * A230199 A275542 A187559
KEYWORD
nonn,base,less
AUTHOR
Shyam Sunder Gupta, Oct 02 2013
STATUS
approved