OFFSET
1,1
COMMENTS
Union of number 5 and numbers >= 7.
Conjecture: this sequence lists all the positive integers n such that, for some integer k, (sin(k*Pi/n))^2 is irrational. - Lorenzo Sauras Altuzarra, Jan 27 2020
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..14995
MATHEMATICA
Select[Range[3, 71], DivisorSigma[1, #] == Mod[PolygonalNumber@ #, Total@ Complement[Range@ #, Divisors@ #]] &] (* Michael De Vlieger, Jan 28 2020 *)
PROG
(Magma) [n: n in [3..100000] | ((n*(n+1)div 2) mod (n*(n+1)div 2-SumOfDivisors(n))) eq (SumOfDivisors(n))]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, May 29 2014
STATUS
approved