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Revision History for A001147

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Showing entries 1-10 | older changes
Double factorial of odd numbers: a(n) = (2*n-1)!! = 1*3*5*...*(2*n-1).
(history; published version)
#653 by N. J. A. Sloane at Fri Nov 15 23:32:27 EST 2024
STATUS

proposed

approved

#652 by Andrew Howroyd at Wed Nov 13 17:45:17 EST 2024
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editing

proposed

#651 by Andrew Howroyd at Wed Nov 13 17:45:13 EST 2024
FORMULA

G.f. of reciprocals: R(x) = Sum_{n>=0} x^n/a(n) satisfies (1 + x) * R(x) = 1 + 2 * x * R'(x). - Werner Schulte, Nov 04 2024

STATUS

proposed

editing

#650 by Andrew Howroyd at Wed Nov 13 17:35:35 EST 2024
STATUS

editing

proposed

#649 by Andrew Howroyd at Wed Nov 13 17:34:19 EST 2024
FORMULA

G.f. of reciprocals: AR(x) = Sum_{n>=0} x^n/a(n) satisfies (1+x) * AR(x) = 1 + 2 * x * AR'(x). - Werner Schulte, Nov 04 2024

Discussion
Wed Nov 13
17:35
Andrew Howroyd: also see R. J. Mathar, Jul 25 2014 formula above.
#648 by Andrew Howroyd at Wed Nov 13 17:24:16 EST 2024
FORMULA

RG.f.: A(x) = Sum_{n>=0} x^n / a(n) satisfies (1+x) * RA(x) = 1 + 2 * x * RA'(x), where R' is first derivative of R. - Werner Schulte, Nov 04 2024

STATUS

proposed

editing

#647 by Werner Schulte at Mon Nov 04 14:35:23 EST 2024
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editing

proposed

#646 by Werner Schulte at Mon Nov 04 14:34:40 EST 2024
FORMULA

R(x) = Sum_{n>=0} x^n / a(n) satisfies (1+x) * R(x) = 1 + 2 * x * R'(x), where R' is first derivative of R. - Werner Schulte, Nov 04 2024

STATUS

approved

editing

#645 by Andrey Zabolotskiy at Thu Oct 03 11:38:30 EDT 2024
STATUS

editing

approved

#644 by Andrey Zabolotskiy at Thu Oct 03 11:38:26 EDT 2024
COMMENTS

a(n) = the number of relaxed compacted binary trees of right height at most one of size n. A relaxed compacted binary tree of size n is a directed acyclic graph consisting of a binary tree with n internal nodes, one leaf, and n pointers. It is constructed from a binary tree of size n, where the first leaf in a post-order traversal is kept and all other leaves are replaced by pointers. These links may point to any node that has already been visited by the post-order traversal. The right height is the maximal number of right-edges (or right children) on all paths from the root to any leaf after deleting all pointers. The numer number of unbounded relaxed compacted binary trees of size n is A082161(n). See the Genitrini et al. link. - Michael Wallner, Jun 20 2017

STATUS

approved

editing