

A117885


Numbers n such that a regular (n^3n)gon can be constructed by means of a ruler and compass.


0




OFFSET

1,1


COMMENTS

Gauss shows a regular ngon can be constructed (with Euclidean tools) iff n is a product of 2^k*(distinct Fermat primes).


LINKS



FORMULA

n^3  n = (n1)*n*(n+1).


EXAMPLE

a(1)=2 because 2^3  2 = 6 = 1*2*3, and a regular hexagon can be constructed by ruler and compass.


PROG

(PARI) for(n=1, 10^4, nn= n^3n; my(t=eulerphi(nn)); if(t/2^valuation(t, 2)==1, print1(n, ", "))); \\ after PARI in A003401; Michel Marcus, Oct 11 2017


CROSSREFS



KEYWORD

nonn,fini,full


AUTHOR



STATUS

approved



