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A028835
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Numbers whose iterated sum of digits is a prime.
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6
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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
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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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
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LINKS
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EXAMPLE
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38 -> 3 + 8 = 11 -> 1 + 1 = 2 is a prime.
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MATHEMATICA
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PROG
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(Haskell)
import Data.List (findIndices)
a028835 n = a028835_list !! (n-1)
a028835_list = findIndices (`elem` [2, 3, 5, 7]) $ map a010888 [0..]
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CROSSREFS
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KEYWORD
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nonn,base,easy,nice
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AUTHOR
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EXTENSIONS
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Extended (and corrected) by Scott Lindhurst (ScottL(AT)alumni.princeton.edu)
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STATUS
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approved
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