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 A007622 Consider Leibniz's harmonic triangle (A003506) and look at the non-boundary terms. Sequence gives numbers appearing in denominators, sorted. (Formerly M4096) 12
 6, 12, 20, 30, 42, 56, 60, 72, 90, 105, 110, 132, 140, 156, 168, 182, 210, 240, 252, 272, 280, 306, 342, 360, 380, 420, 462, 495, 504, 506, 552, 600, 630, 650, 660, 702, 756, 812, 840, 858, 870, 930, 992, 1056, 1092, 1122, 1190, 1260, 1320, 1332 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No term is prime, about 80% are abundant, but the first few deficient are: 105, 110, 182, 495, 506, 1365, 1406, 1892, 2162, 2756, 2907, 3422, 3782, 4556, 5313, .... - Robert G. Wilson v, Aug 16 2010 A002943 = (6, 20, 42, 72, 110, 156, 210, 272, 342, 420, 506, 600, 702, ...) is a subsequence: indeed, this is every second denominator of the first differences of the sequence 1/n. - M. F. Hasler, Oct 11 2015 REFERENCES L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 83, Problem 25. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). D. Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, 35. LINKS Robert G. Wilson v, Table of n, a(n) for n = 1..1217. Eric Weisstein's World of Mathematics, Leibniz Harmonic Triangle. MATHEMATICA L[n_, 1] := 1/n; L[n_, m_] := L[n, m] = L[n - 1, m - 1] - L[n, m - 1]; Take[ Union[ Flatten[ Table[ 1/L[n, m], {n, 3, 150}, {m, 2, Floor[n/2 + .5]}]]], 65] t[n_, k_] := Denominator[n!*k!/(n + k + 1)!]; Take[ DeleteDuplicates@ Rest@ Sort@ Flatten@ Table[t[n - k, k], {n, 2, 150}, {k, n/2 + 1}], 65] (* Robert G. Wilson v, Jun 12 2014 *) CROSSREFS Sequence in context: A080714 A116368 A290467 * A180291 A056930 A326378 Adjacent sequences:  A007619 A007620 A007621 * A007623 A007624 A007625 KEYWORD nonn AUTHOR EXTENSIONS More terms from Larry Reeves (larryr(AT)acm.org), Jul 25 2000. Rechecked Jun 27 2003. STATUS approved

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Last modified January 29 08:04 EST 2020. Contains 331337 sequences. (Running on oeis4.)