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A213653
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Least semiprime whose digital sum is n, or 0 if no such integer exists.
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2
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0, 10, 10001, 21, 4, 14, 6, 25, 26, 9, 46, 38, 39, 49, 77, 69, 169, 278, 0, 289, 299, 489, 589, 689, 699, 799, 899, 0, 2899, 3899, 4989, 5899, 5999, 6999, 7999, 9899, 0, 19999, 29999, 48999, 58999, 68999, 69999, 88999, 99899, 0, 299899, 398999, 589989
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OFFSET
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0,2
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COMMENTS
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a(9k) = 0 for all k>1.
I conjecture that all terms > 278, except for 10001, end in the digit "9". What is the next term a(n) > 69 violating monotony, i.e., such that a(n) < a(n-1)? M. F. Hasler, Jun 17 2012
a(88) = 7999999999 < a(87) = 8899899999. - Alois P. Heinz, Jun 17 2012
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LINKS
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MATHEMATICA
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semiPrimeQ[n_] := PrimeOmega[n] == 2; t = Table[0, {100}]; k = 1; While[k < 10^7, If[ semiPrimeQ@ k, s = Plus @@ IntegerDigits@ k; If[s < 101 && t[[s]] == 0, t[[s]] = k; Print[{s, k}]]]; k++]
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PROG
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CROSSREFS
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KEYWORD
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easy,base,nonn
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AUTHOR
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EXTENSIONS
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a(0)-a(62) double-checked with given PARI code by M. F. Hasler, Jun 17 2012
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STATUS
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approved
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