OFFSET
1,1
COMMENTS
It appears that for all k>1, a(k) is a multiple of 4.
It also appears that all Cyclotomic Polynomials, Phi[k](x), where k is a multiple of 4 have no odd powers of x. For example, Phi[20](x)=x^8-x^6+x^4-x^2+1. This implies that Phi[k](x)=Phi[k](-x), where k is a multiple of 4. - Robert Price, Apr 14 2012
LINKS
Robert Price, Table of n, a(n) for n = 1..49
Yves Gallot, Cyclotomic polynomials and prime numbers
MATHEMATICA
Select[ Range[3, 5000], PrimeQ[ Cyclotomic[#, -4]] &] (* Robert G. Wilson v, Mar 25 2012 *)
PROG
(PARI) for( i=1, 999, ispseudoprime( polcyclo(i, -4)) && print1( i", ")) /* use ...subst(polcyclo(i), x, -4)... in PARI < 2.4.2 */
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Apr 03 2008
EXTENSIONS
a(36)-a(49) from Robert Price, Apr 07 2012
STATUS
approved