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A304275 Sum_{k=1..n} gcd(k,n) / cos(Pi*k/n)^2 for odd n. 1
1, 11, 29, 55, 105, 131, 181, 319, 305, 379, 605, 551, 745, 963, 869, 991, 1441, 1595, 1405, 1991, 1721, 1891, 3045, 2255, 2737, 3355, 2861, 3799, 4169, 3539, 3781, 5775, 5249, 4555, 6061, 5111, 5401, 8195, 7205, 6319, 8721, 6971, 8845 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Hugo Pfoertner, Table of n, a(n) for n = 1..1000

Nikolai Osipov (Proposer), Problem 12003, Amer. Math. Monthly 124 (No. 8, Oct. 2017), page 754.

PROG

(PARI) a(n) = n = 2*n-1; round(sum(k=1, n, gcd(k, n) / cos(Pi*k/n)^2)); \\ Michel Marcus, May 10 2018

CROSSREFS

Sequence in context: A082108 A024846 A024842 * A031072 A193880 A138248

Adjacent sequences:  A304272 A304273 A304274 * A304276 A304277 A304278

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, May 10 2018

STATUS

approved

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Last modified September 26 20:33 EDT 2022. Contains 357034 sequences. (Running on oeis4.)