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A247416 Number of friezes of type B_n. 1
2, 6, 21, 75, 273, 1008, 3762, 14158, 53635, 204270, 781378, 2999906, 11553234, 44612760, 172671925, 669679793, 2601913466, 10125418060, 39459828905, 153977743500, 601545298200, 2352559491900, 9209476821105, 36084150102001, 141499349638556, 555292275455022, 2180689496523468, 8569380062230708 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..28.

B. Fontaine and P.-G. Plamondon, Counting friezes in type D_n, arXiv:1409.3698 [math.CO], 2014.

FORMULA

a(n) = sum_{m=1..floor(sqrt(n+1))} binomial(2n-m^2+1,n).

PROG

(PARI) a(n) = sum(m=1, sqrtint(n+1), binomial(2*n-m^2+1, n) ); \\ Joerg Arndt, Sep 16 2014

CROSSREFS

Cf. A000108, A000984 and A247415, the number of friezes of type A_n, C_n and D_n.

Sequence in context: A116743 A294816 A263790 * A105872 A304781 A148490

Adjacent sequences:  A247413 A247414 A247415 * A247417 A247418 A247419

KEYWORD

nonn

AUTHOR

Bruce Fontaine, Sep 16 2014

STATUS

approved

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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)