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A061780
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Number of solutions to x+y+z = 0 mod (2n+1) such that x,y,z are units modulo 2n+1 i.e. gcd(x,2n+1) = gcd(y,2n+1) = gcd(z,2n+1) = 1.
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0
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2, 12, 30, 18, 90, 132, 24, 240, 306, 60, 462, 300, 162, 756, 870, 180, 360, 1260, 264, 1560, 1722, 216, 2070, 1470, 480, 2652, 1080, 612, 3306, 3540, 540, 1584, 4290, 924, 4830, 5112, 600, 2700, 6006, 1458, 6642, 2880, 1512, 7656, 3960, 1740, 3672, 9120
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n) is multiplicative and if 2n+1=p^k is a prime power with p an odd prime then a(n) = p^(2k-2) * (p^2 - 3p + 2).
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EXAMPLE
| The only solutions modulo 3 in units are 1+1+1 = 0 mod 3, 2+2+2 = 0 mod 3 so the first element of the sequence is 2.
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CROSSREFS
| Sequence in context: A119201 A164876 A034318 * A156021 A067348 A002939
Adjacent sequences: A061777 A061778 A061779 * A061781 A061782 A061783
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KEYWORD
| nonn,mult
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AUTHOR
| Ahmed Fares (ahmedfares(AT)my-deja.com), Jun 22 2001
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 23 2001
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