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A234536
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Numbers k such that k+1 is a divisor of 3^k + 5^k.
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3
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1, 3, 7, 75, 2355, 11475, 31995, 57075, 80311, 196185, 215325, 335115, 991875, 1009545, 1038375, 1169715, 1185675, 1193655, 3507751, 5503095, 8412525, 8618475, 8670915, 9513075, 11384343, 12689415, 13587735, 13708695, 14101815, 14841255, 16002525, 17409015, 21856635, 22195875, 22307805, 25948755
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OFFSET
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1,2
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COMMENTS
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It is an open problem to find all numbers k such that (k+1)*(k-1) is a divisor of 3^k + 5^k.
In particular, it is not known if the intersection of this sequence and A234535 equals {3}. - Max Alekseyev, May 19 2015
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LINKS
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Amiram Eldar, Table of n, a(n) for n = 1..600
Daniel Kohen et al., On Polynomials dividing Exponentials, MathOverflow.
Byron Schmuland et al., Find all positive integers n such that 3^n + 5^n is divisible by n^2 - 1, Math StackExchange.
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MATHEMATICA
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Select[Range[10^6], Mod[PowerMod[3, #, # + 1] + PowerMod[5, #, # + 1], # + 1] == 0 &]
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PROG
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(PARI) isok(k) = Mod(3, k+1)^k + Mod(5, k+1)^k == 0; \\ Michel Marcus, Aug 04 2021
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CROSSREFS
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Cf. A234535.
Sequence in context: A119572 A172995 A325476 * A103737 A108537 A219292
Adjacent sequences: A234533 A234534 A234535 * A234537 A234538 A234539
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KEYWORD
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nonn
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AUTHOR
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Siad Daboul, Dec 27 2013
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EXTENSIONS
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a(1) inserted by Amiram Eldar, Jul 31 2021
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STATUS
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approved
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