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 A024812 Numbers n for which there is exactly one positive integer m such that n = floor(cot(Pi/(2m))). 4
 2, 4, 7, 9, 11, 14, 16, 18, 21, 23, 25, 28, 30, 32, 34, 37, 39, 41, 44, 46, 48, 51, 53, 55, 58, 60, 62, 65, 67, 69, 72, 74, 76, 79, 81, 83, 86, 88, 90, 93, 95, 97, 100, 102, 104, 107, 109, 111, 114, 116, 118, 121, 123, 125, 128, 130, 132, 135, 137, 139, 142, 144, 146, 149, 151, 153 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture (verified for k <= 10^6 by M. F. Hasler): A024812(k) = (A024813(k)+k-1)/2, k=1,2,.... - L. Edson Jeffery, Mar 21 2013 LINKS FORMULA a(k) = floor(cot(Pi/(2*A024813(k)))). - L. Edson Jeffery, Mar 21 2013 Conjecture: a(n) = a(n-1) + a(n-3) - a(n-4); g.f.: x*(x^15-x^14+3*x^2+2*x+2) / ((x-1)^2*(x^2+x+1)). - Colin Barker, Jan 03 2014 MATHEMATICA f[n_] := Floor[Cot[Pi/(2 n)]]; f[ Select[ Range[2, 245], f[# - 1] < f[#] < f[# + 1] &]] (* Robert G. Wilson v, Mar 27 2013 *) PROG (PARI) {my(f(m)=floor(cotan(Pi/(2*m)))); for(m=2, 999, f(m-1)

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Last modified August 11 23:45 EDT 2020. Contains 336434 sequences. (Running on oeis4.)