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A113930
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Numbers k such that sigma(k) and phi(k) are both triangular numbers.
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1
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1, 2, 22, 3051, 3219, 3393, 5057, 8653, 75618, 95675, 100503, 102949, 104714, 287826, 438547, 522339, 537159, 688050, 2191200, 2317118, 2418548, 2507683, 2599128, 3212964, 4534573, 5367797, 6047913, 6302639, 7689149, 13758296, 14380145, 15342050, 16148979
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OFFSET
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1,2
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COMMENTS
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phi(k) = A000010(k) is the Euler totient function, while sigma(k) = A000203(k) is the sum of divisors of k.
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LINKS
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EXAMPLE
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sigma(100503) = 156520 = T(559) and phi(100503) = 61776 = T(351).
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PROG
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(PARI) isok(n) = ispolygonal(sigma(n), 3) && ispolygonal(eulerphi(n), 3); \\ Michel Marcus, Jan 26 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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