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Search: id:A060866
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| A060866 |
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Sum of (d+d') over all unordered pairs (d,d') with d*d' = n. |
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+0
3
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| 2, 3, 4, 9, 6, 12, 8, 15, 16, 18, 12, 28, 14, 24, 24, 35, 18, 39, 20, 42, 32, 36, 24, 60, 36, 42, 40, 56, 30, 72, 32, 63, 48, 54, 48, 97, 38, 60, 56, 90, 42, 96, 44, 84, 78, 72, 48, 124, 64, 93, 72, 98, 54, 120, 72, 120, 80, 90, 60, 168, 62, 96, 104, 135, 84, 144, 68, 126, 96
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Note that if n is not a square then a(n) = sigma(n), the sum of divisors of n, otherwise a(n) = sigma(n) + sqrt(n). [From Omar E. Pol (info(AT)polprimos.com), Jun 23 2009]
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FORMULA
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a(n) = A066839(n)+A070038(n) = A000203(n)+A037213(n). G.f.: Sum_{n>0} n*x^n*(x^(n*(n-1))-x^(n^2)+1)/(1-x^n). - Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 25 2003
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EXAMPLE
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a(4)=9 because pairs of factors are 1*4 and 2*2 and 1+4+2+2=9. a(6)=12 because pairs of factors are 1*6 and 2*3 and 1+6+2+3=12.
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CROSSREFS
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Cf. A060872.
Sequence in context: A106443 A091205 A106447 this_sequence A064478 A111798 A115305
Adjacent sequences: A060863 A060864 A060865 this_sequence A060867 A060868 A060869
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KEYWORD
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nonn,easy
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), May 04 2001
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EXTENSIONS
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More terms from Erich Friedman (efriedma(AT)stetson.edu), Jun 03 2001
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