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 A326608 Numbers m such that m | A000385(m-1) = Sum_{k=1..m-1} sigma(k) * sigma(m-k). 1
 1, 3, 40, 84, 124, 318, 496, 672, 732, 790, 1320, 1488, 3154, 4464, 5271, 8128, 9156, 9888, 10880, 13392, 14760, 16392, 17019, 22366, 24384, 39424, 57240, 67488, 68237, 73276, 93825, 95728, 106428, 115330, 128982, 138176, 143256, 143780, 144210, 154432, 156360 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 1 is in the sequence assuming A000385(0) = 0. The corresponding quotients are 0, 2, 723, 3376, 7196, 48834, 116655, 222646, 263221, 294168, 865608, ... Includes all the even perfect numbers except for 6 and 28. The only prime number in the sequence is 3. This follows from formula for A000385 given by Robert Israel. - Luis H. Gallardo, Jun 17 2020 LINKS Amiram Eldar, Table of n, a(n) for n = 1..500 EXAMPLE 3 is in the sequence since 3 is a divisor for A000385(3-1) = 6. MATHEMATICA aQ[n_] := Divisible[5 * DivisorSigma[3, n] - (6n - 1) * DivisorSigma[1, n], 12n]; Select[Range[2*10^5], aQ] CROSSREFS Cf. A000203, A000385, A000396. Sequence in context: A101014 A262036 A041347 * A160659 A197247 A065815 Adjacent sequences: A326605 A326606 A326607 * A326609 A326610 A326611 KEYWORD nonn AUTHOR Amiram Eldar, Oct 18 2019 STATUS approved

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Last modified September 24 10:56 EDT 2023. Contains 365579 sequences. (Running on oeis4.)