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A349751
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Odd numbers k such that sigma(k) == -k (mod 3), where sigma is the sum of divisors function.
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3
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7, 13, 15, 19, 31, 33, 37, 43, 45, 51, 61, 67, 69, 73, 79, 87, 97, 99, 103, 105, 109, 123, 127, 135, 139, 141, 147, 151, 153, 157, 159, 163, 165, 175, 177, 181, 193, 195, 199, 207, 211, 213, 223, 229, 231, 241, 249, 255, 261, 267, 271, 277, 283, 285, 297, 303, 307, 313, 315, 321, 325, 331, 337, 339, 345, 349, 357
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OFFSET
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1,1
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COMMENTS
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Odd numbers k for which A155085(k) is a multiple of 3.
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LINKS
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EXAMPLE
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7 is present as 7 mod 3 = +1, while sigma(7) = 8, and 8 mod 3 = 2, i.e., -1.
45 is present as 45 mod 3 = 0, while sigma(45) = 78, and 78 mod 3 = 0 as well.
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MATHEMATICA
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Select[Range[1, 360, 2], Divisible[DivisorSigma[1, #] + #, 3] &] (* Amiram Eldar, Dec 01 2021 *)
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PROG
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(PARI) isA349751(n) = ((n%2)&&0==(sigma(n)+n)%3);
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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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