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 A330866 a(n) = Sum_{d|n, d
 0, 2, 6, 16, 20, 48, 42, 88, 90, 140, 110, 264, 156, 280, 300, 416, 272, 594, 342, 720, 588, 704, 506, 1248, 700, 988, 972, 1400, 812, 1920, 930, 1824, 1452, 1700, 1540, 2952, 1332, 2128, 2028, 3280, 1640, 3696, 1806, 3432, 3240, 3128, 2162, 5472, 2646, 4350, 3468 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(p^k) = p^k * (p^(k+1) - p*(k+1) + k) / (p-1), where p is prime and k is a positive integer. EXAMPLE a(6) = 48; The proper divisors of 6 are 1, 2 and 3. We have (6/1)*(6-1) + (6/2)*(6-2) + (6/3)*(6-3) = 30 + 12 + 6 = 48. MATHEMATICA Table[Sum[(n/i) (n-i) (1 - Ceiling[n/i] + Floor[n/i]), {i, n-1}], {n, 80}] PROG (PARI) a(n)={sumdiv(n, d, (n-d)*n/d)} \\ Andrew Howroyd, Apr 28 2020 CROSSREFS Cf. A001065. Sequence in context: A082374 A085226 A260376 * A071522 A192532 A230853 Adjacent sequences: A330863 A330864 A330865 * A330867 A330868 A330869 KEYWORD nonn,easy AUTHOR Wesley Ivan Hurt, Apr 28 2020 STATUS approved

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Last modified December 3 13:56 EST 2022. Contains 358534 sequences. (Running on oeis4.)