

A028835


Numbers whose iterated sum of digits is a prime.


6



2, 3, 5, 7, 11, 12, 14, 16, 20, 21, 23, 25, 29, 30, 32, 34, 38, 39, 41, 43, 47, 48, 50, 52, 56, 57, 59, 61, 65, 66, 68, 70, 74, 75, 77, 79, 83, 84, 86, 88, 92, 93, 95, 97, 101, 102, 104, 106, 110, 111, 113, 115, 119, 120, 122, 124, 128, 129, 131, 133, 137, 138, 140, 142, 146, 147, 149, 151, 155, 156
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OFFSET

1,1


COMMENTS

Also numbers k such that k mod 9 is an element of {2,3,5,7}. Hence as n tends to infinity, a(n)/n converges to 9/4 quite rapidly.  Stefan Steinerberger, Apr 23 2006


LINKS



EXAMPLE

38 > 3 + 8 = 11 > 1 + 1 = 2 is a prime.


MATHEMATICA



PROG

(Haskell)
import Data.List (findIndices)
a028835 n = a028835_list !! (n1)
a028835_list = findIndices (`elem` [2, 3, 5, 7]) $ map a010888 [0..]


CROSSREFS



KEYWORD

nonn,base,easy,nice


AUTHOR



EXTENSIONS

Extended (and corrected) by Scott Lindhurst (ScottL(AT)alumni.princeton.edu)


STATUS

approved



