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A152991
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a(n) = sigma(n) - pi(n).
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3
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1, 2, 2, 5, 3, 9, 4, 11, 9, 14, 7, 23, 8, 18, 18, 25, 11, 32, 12, 34, 24, 28, 15, 51, 22, 33, 31, 47, 20, 62, 21, 52, 37, 43, 37, 80, 26, 48, 44, 78, 29, 83, 30, 70, 64, 58, 33, 109, 42, 78, 57, 83, 38, 104, 56, 104, 64, 74, 43, 151, 44, 78, 86, 109, 66, 126, 49, 107, 77, 125, 52
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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a(15) = 24 - 6 = 18 because the sum of the divisors of 15 is 1 + 3 + 5 + 15 = 24 and there are 6 primes not exceeding 15 (2, 3, 5, 7, 11 and 13). - Emeric Deutsch, Dec 29 2008
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MAPLE
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with(numtheory): seq(sigma(n)-pi(n), n = 1 .. 80); # Emeric Deutsch, Dec 29 2008
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MATHEMATICA
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Table[DivisorSigma[1, n]-PrimePi[n], {n, 80}] (* Harvey P. Dale, Oct 20 2021 *)
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PROG
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(PARI) a(n) = sigma(n) - primepi(n); \\ Michel Marcus, Jun 18 2019
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CROSSREFS
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KEYWORD
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easy,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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