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Search: id:A117948
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| A117948 |
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Sum of the divisors of pentagonal numbers. |
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+0
2
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| 0, 1, 6, 28, 36, 48, 72, 144, 168, 182, 180, 372, 576, 280, 336, 864, 720, 558, 702, 1120, 1080, 1024, 1008, 1296, 2016, 1178, 1344, 3600, 2016, 1320, 2160, 2304, 3720, 2736, 1836, 4704, 4212, 2736, 2280, 5040, 6048, 2604, 4992, 5588, 4752, 5304, 3312
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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See also: A000326 Pentagonal numbers: n(3n-1)/2. A000203 sigma(n) = sum of divisors of n. Also called sigma_1(n). A074285 Sum of the divisors of n-th triangular number. A117949 Indices of pentagonal numbers whose sum of divisors is square.
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FORMULA
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a(n)=sigma(n(3n-1)/2), where sigma is the sum of divisors function. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 15 2006
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EXAMPLE
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a(5)=48 because the divisors of 5*(3*5-1)/2=35 are 1,5,7, and 35, having sum 48.
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MAPLE
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with(numtheory): seq(sigma(n*(3*n-1)/2), n=0..46); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 15 2006
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CROSSREFS
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Cf. A000203, A000203, A074285, A117949.
Sequence in context: A105402 A145551 A083865 this_sequence A071834 A055196 A120624
Adjacent sequences: A117945 A117946 A117947 this_sequence A117949 A117950 A117951
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 04 2006
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