OFFSET
1,2
COMMENTS
a(n) is the number of terms of A003401, except its first two degenerate case terms, that are less than 2^n + 1.
LINKS
Jinyuan Wang, Table of n, a(n) for n = 1..10000
Raymond Clare Archibald, Remarks on Klein's "Famous Problems of Elementary Geometry", The American Mathematical Monthly, Vol. 21, No. 8 (Oct., 1914), pp. 247-259.
Leonard E. Dickson, On the number of inscriptible regular polygons, Bull. Amer. Math. Soc. 3 (1894), 123-125.
Wilfrid Keller, Prime factors k.2^n + 1 of Fermat numbers F_m
FORMULA
a(n) = (n-1)*(n+2)/2 if n < 32, otherwise 32*n-497 if n < 2^33.
EXAMPLE
For n=2, there are 2 such polygons, those with 3 and 4 sides, below 2^2+1 = 5.
PROG
(PARI) a(n) = if(n < 32, (n-1)*(n+2)/2, if(n < 2^33, 32*n-497));
(PARI) a(n) = {i = 2^n; j = 2*n - 2; k = 1; while(i > A045544(k) && k < 31, k++; j+=floor(log(i/A045544(k))/log(2))+1); j; } \\ Jinyuan Wang, Jul 29 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 28 2016
STATUS
approved