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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 (list; graph; refs; listen; history; text; internal format)
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

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

Cf. A038194, A002385.

Sequence in context: A032759 A142711 A093338 * A230199 A275542 A187559

Adjacent sequences:  A229872 A229873 A229874 * A229876 A229877 A229878

KEYWORD

nonn,base,less

AUTHOR

Shyam Sunder Gupta, Oct 02 2013

STATUS

approved

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Last modified July 5 07:06 EDT 2020. Contains 335460 sequences. (Running on oeis4.)