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 A168012 a(n) = sum of all divisors of all numbers k such that n^2 <= k < (n+1)^2. 4
 8, 48, 133, 302, 516, 923, 1346, 2038, 2768, 3891, 4810, 6572, 7959, 10066, 12186, 14944, 17261, 21210, 23992, 28497, 32550, 37742, 42111, 48906, 54252, 61280, 68153, 76958, 82942, 94661, 101882, 113082, 123794, 135583, 145630, 161526 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo Xausa, Table of n, a(n) for n = 1..1000 EXAMPLE a(2) = 48 because the numbers k are 4,5,6,7 and 8 (since 2^2 <= k < 3^2) and sigma(4) + sigma(5) + sigma(6) + sigma(7) + sigma(8) = 7 + 6 + 12 + 8 + 15 = 48, where sigma(n) is the sum of divisors of n (see A000203). MATHEMATICA A168012[n_]:=Sum[DivisorSigma[1, k], {k, n^2, (n+1)^2-1}]; Array[A168012, 50] (* Paolo Xausa, Oct 23 2023 *) PROG (PARI) a(n)=sum(k=n^2, (n+1)^2-1, sigma(k)) \\ Franklin T. Adams-Watters, May 14 2010 (Python) def A168012(n): a, b = n*(n+2), (n-1)*(n+1) return (sum((q:=a//k)*((s:=k<<1)+q+1)-(r:=b//k)*(s+r+1) for k in range(1, n))>>1)+5*n+3 # Chai Wah Wu, Oct 23 2023 CROSSREFS Cf. A000203, A024916, A168010, A168011, A168013. Sequence in context: A152750 A121355 A227499 * A222816 A280056 A035471 Adjacent sequences: A168009 A168010 A168011 * A168013 A168014 A168015 KEYWORD nonn AUTHOR Omar E. Pol, Nov 16 2009 EXTENSIONS More terms from Franklin T. Adams-Watters, May 14 2010 STATUS approved

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Last modified December 11 09:49 EST 2023. Contains 367722 sequences. (Running on oeis4.)