A079130 Primes such that iterated sum-of-digits (A038194) is a square.

13, 19, 31, 37, 67, 73, 103, 109, 127, 139, 157, 163, 181, 193, 199, 211, 229, 271, 283, 307, 337, 373, 379, 397, 409, 433, 463, 487, 499, 523, 541, 571, 577, 607, 613, 631, 643, 661, 733, 739, 751, 757, 769, 787, 811, 823, 829, 859, 877, 883, 919, 937, 967

Offset: 1

Author

Klaus Brockhaus, Dec 28 2002

Keywords

• nonn
• easy
• base

Comments

Primes which are 1 or 4 mod 9. - Charles R Greathouse IV, Sep 04 2014

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A078403, A079131, A079132.

Programs

Maple

select(isprime,map(t -> (9*t+1,9*t+4),[$1..1000]));  # Robert Israel, Sep 04 2014

Mathematica

sQ[n_]:=MemberQ[{1,4,9},NestWhile[Total[IntegerDigits[#]]&,n,#>9&]]; Select[Prime[Range[300]],sQ] (* Harvey P. Dale, Dec 06 2012 *)

PARI

forprime(p=2,1000,if(issquare(p%9),print1(p,",")))

Formula

a(n) ~ 3n log n. - Charles R Greathouse IV, Sep 04 2014