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A327703 a(n) = (binomial(n,floor(n/2)))/(greatest common divisor of all numbers in n-th row of Pascal's triangle excluding 1 and n). 0
1, 1, 4, 5, 5, 21, 84, 42, 84, 132, 264, 6435, 6435, 715, 2860, 4862, 9724, 352716, 705432, 58786, 117572, 1040060, 2080120, 6686100, 13372200, 2674440, 5348880, 9694845, 9694845, 583401555 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,3

COMMENTS

For all values of a(n), where a(n) is not equal to A001405(n), n is either: a prime, a power of a prime, a prime +1 or a power of a prime +1.

LINKS

Table of n, a(n) for n=4..33.

FORMULA

a(n) = A001405(n)/A328202(n).

EXAMPLE

For n = 17, a(17) = A001405(17)/A328202(17) = 24310/34 = 715.

MATHEMATICA

a[n_] := Binomial[n, Floor[n/2]]/GCD @@ Binomial[n, Range[2, n/2]]; Array[a, 30, 4] (* Amiram Eldar, Oct 24 2019 *)

PROG

(PARI) a(n) = binomial(n, n\2)/gcd(vector((n+1)\2-1, k, binomial(n, k+1))); \\ Michel Marcus, Oct 24 2019

CROSSREFS

Cf. A001405, A328202.

Sequence in context: A120132 A154914 A154916 * A077061 A072508 A075566

Adjacent sequences:  A327700 A327701 A327702 * A327704 A327705 A327706

KEYWORD

nonn

AUTHOR

Joel Kaufmann, Oct 24 2019

STATUS

approved

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Last modified February 25 05:01 EST 2020. Contains 332217 sequences. (Running on oeis4.)