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A268619 a(n) = (1/n^2) * Sum_{d|n} moebius(n/d)*binomial(2*d,d). 6
2, 1, 2, 4, 10, 25, 70, 200, 600, 1845, 5830, 18772, 61542, 204659, 689410, 2347920, 8074762, 28009524, 97909318, 344615860, 1220539390, 4347310451, 15564141262, 55985418344, 202256970300, 733607281875, 2670698800548, 9755982857964, 35751803209918, 131405090455065, 484316704740126, 1789672012052256 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

6*a(n) is divisible by n (cf. A268592).

LINKS

Table of n, a(n) for n=1..32.

FORMULA

a(n) = (1/n^2)* Sum_{d|n} A008683(n/d)*A000984(d).

a(n) = A007727(n)/n^2 = A045630(n)*2/n^2 = A060165(n)/n = A022553(n)*2/n.

PROG

(PARI) { a(n) = sumdiv(n, d, moebius(n/d)*binomial(2*d, d))/n^2; }

CROSSREFS

Cf. A268617

Sequence in context: A135547 A146307 A063894 * A024500 A318870 A000087

Adjacent sequences:  A268616 A268617 A268618 * A268620 A268621 A268622

KEYWORD

nonn

AUTHOR

Max Alekseyev, Feb 09 2016

STATUS

approved

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Last modified October 20 01:39 EDT 2018. Contains 316378 sequences. (Running on oeis4.)