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Search: id:A078708
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| A078708 |
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Sum of divisors d of n such that n/d is not congruent to 0 mod 3. |
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+0
1
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| 1, 3, 3, 7, 6, 9, 8, 15, 9, 18, 12, 21, 14, 24, 18, 31, 18, 27, 20, 42, 24, 36, 24, 45, 31, 42, 27, 56, 30, 54, 32, 63, 36, 54, 48, 63, 38, 60, 42, 90, 42, 72, 44, 84, 54, 72, 48, 93, 57, 93, 54, 98, 54, 81, 72, 120, 60, 90, 60, 126, 62, 96, 72, 127, 84, 108, 68, 126, 72, 144
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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G.f.: Sum_{k>0} x^k*(1+x^k)^2*(1+x^(2*k))/(1-x^(3*k))^2.
a(n)=(A000203(3*n)-A000203(n))/3. - Vladeta Jovovic (vladeta(AT)Eunet.yu), Dec 22 2003
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PROGRAM
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(PARI) for(n=1, 70, d=divisors(n); s=0; for(j=1, matsize(d)[2], if((n/d[j])%3>0, s=s+d[j])); print1(s, ", "))
(PARI) a(n)=sumdiv(n, d, if((n/d)%3, 1, 0)*d)
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CROSSREFS
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Cf. A046913, A035191.
Sequence in context: A106477 A098043 A045773 this_sequence A096273 A069981 A000199
Adjacent sequences: A078705 A078706 A078707 this_sequence A078709 A078710 A078711
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KEYWORD
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mult,easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Dec 18 2002
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EXTENSIONS
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Extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Benoit Cloitre, Dec 20 2002
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