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A064427
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a(n) = n + (number of primes < n).
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4
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1, 2, 4, 6, 7, 9, 10, 12, 13, 14, 15, 17, 18, 20, 21, 22, 23, 25, 26, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 40, 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 55, 56, 58, 59, 60, 61, 63, 64, 65, 66, 67, 68, 70, 71, 72, 73, 74, 75, 77, 78, 80, 81, 82
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OFFSET
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1,2
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COMMENTS
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Numbers that are not the sum of k and the k-th prime for any k >= 1. (End)
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LINKS
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FORMULA
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For n > 1: a(n) = n + A000720(n-1).
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MATHEMATICA
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a[n_] := PrimePi[a[n-1]]+n; a[1]=1
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PROG
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(Haskell)
a064427 1 = 1
a064427 n = a000720 (n - 1) + toInteger n
(PARI) a(n) = if (n==1, 1, primepi(n-1)+n); \\ Michel Marcus, Feb 13 2016
(Magma) [1] cat [#PrimesUpTo(n-1)+n: n in [2..100]]; // Vincenzo Librandi, Feb 13 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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