%I
%S 2,3,5,7,11,12,14,16,20,21,23,25,29,30,32,34,38,39,41,43,47,48,50,52,
%T 56,57,59,61,65,66,68,70,74,75,77,79,83,84,86,88,92,93,95,97,101,102,
%U 104,106,110,111,113,115,119,120,122,124,128,129,131,133,137,138,140,142,146,147,149,151,155,156
%N Numbers n such that iterated sum of digits of n is a prime.
%C Also numbers n such that n modulo 9 is an element of {2,3,5,7}. Hence as n tends to infinity, a(n)/n converges against 9/4 quite rapidly.  _Stefan Steinerberger_, Apr 23 2006
%H Reinhard Zumkeller, <a href="/A028835/b028835.txt">Table of n, a(n) for n = 1..10000</a>
%e 38 > 3 + 8 = 11 > 1 + 1 = 2 is a prime.
%t Select[Range[200], PrimeQ[Mod[ #, 9]] &] (* _Stefan Steinerberger_, Apr 23 2006 *)
%o (Haskell)
%o import Data.List (findIndices)
%o a028835 n = a028835_list !! (n1)
%o a028835_list = findIndices (`elem` [2,3,5,7]) $ map a010888 [0..]
%o  _Reinhard Zumkeller_, Oct 21 2011
%Y Cf. A010888, A028834, A028843.
%K nonn,base,easy,nice
%O 1,1
%A _N. J. A. Sloane_
%E Extended (and corrected) by Scott Lindhurst (ScottL(AT)alumni.princeton.edu)
