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A107350
Number of isogons with a certain property.
3
1, 4, 34, 346, 3965, 48396, 615966, 8082457, 108545916, 1484716135, 20612084010, 289688970195, 4113620233260, 58930127470164, 850641610106596, 12360278974175769, 180648953113093368, 2653875476976308643, 39167191622334514398, 580439539153823110678, 8633956582855204662785
OFFSET
1,2
COMMENTS
This and A060005 appear in the reference as incidental sequences when computing A007219.
LINKS
L. Sallows, M. Gardner, R. K. Guy and D. E. Knuth, Serial isogons of 90 degrees, Math. Mag. 64 (1991), 315-324.
FORMULA
product[ {1+x^(2i+1)},i=0,1,...,4n-1] = 1+...+2*a(n)*x^(8n^2)+.... (g.f.). - R. J. Mathar, May 08 2007
a(n) = A292476(2*n)/2. - Seiichi Manyama, Sep 18 2017
MAPLE
A107350 := proc(n) res := 1 ; for i from 0 to 4*n-1 do res := taylor(res*(1+x^(2*i+1)), x=0, 8*n^2+1) ; od ; coeftayl(res, x=0, 8*n^2)/2 ; end: for n from 1 to 25 do printf("%d, ", A107350(n)) ; od ; # R. J. Mathar, May 08 2007
MATHEMATICA
a[n_] := SeriesCoefficient[Product[x^(2k - 1) + 1/x^(2k - 1), {k, 1, 4n}], {x, 0, 0}]/2;
Table[a[n], {n, 1, 25}] (* Jean-François Alcover, Mar 10 2023 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, May 23 2005
EXTENSIONS
More terms from R. J. Mathar, May 08 2007
STATUS
approved