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A152991
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a(n) = sigma(n) - pi(n).
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2
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) = A000203(n)-A000720(n). [From Omar E. Pol (info(AT)polprimos.com), Dec 21 2008]
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EXAMPLE
| 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). [From Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 29 2008]
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MAPLE
| with(numtheory): seq(sigma(n)-pi(n), n = 1 .. 80); [From Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 29 2008]
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CROSSREFS
| Cf. A000203, A000720, A152770.
Sequence in context: A071939 A075545 A006307 * A163298 A133440 A160793
Adjacent sequences: A152988 A152989 A152990 * A152992 A152993 A152994
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KEYWORD
| easy,nonn
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AUTHOR
| Omar E. Pol (info(AT)polprimos.com), Dec 19 2008
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EXTENSIONS
| Corrected and extended by Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 29 2008
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