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A046212
First numerator and then denominator of central elements of Leibniz's Harmonic Triangle.
20
1, 1, 1, 6, 1, 30, 1, 140, 1, 630, 1, 2772, 1, 12012, 1, 51480, 1, 218790, 1, 923780, 1, 3879876, 1, 16224936, 1, 67603900, 1, 280816200, 1, 1163381400, 1, 4808643120, 1, 19835652870, 1, 81676217700, 1, 335780006100, 1, 1378465288200, 1
OFFSET
1,4
REFERENCES
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 83, Problem 25.
FORMULA
a(2n+1) = A056040(2n+1) = A100071(2n+1). - M. F. Hasler, Jan 25 2012
CROSSREFS
Cf. A003506.
Cf. A002457.
Sequence in context: A193633 A176289 A118933 * A120105 A120101 A178726
KEYWORD
nonn,easy
EXTENSIONS
More terms from James Sellers, Dec 13 1999
STATUS
approved