A138935 Indices k such that A019323(k)=Phi[k](5) is prime, where Phi is a cyclotomic polynomial.

3, 7, 10, 11, 12, 13, 24, 28, 47, 48, 49, 56, 57, 88, 90, 92, 108, 110, 116, 120, 127, 134, 141, 149, 161, 181, 198, 202, 206, 236, 248, 288, 357, 384, 420, 458, 500, 530, 536, 619, 620, 694, 798, 897, 929, 981, 992, 1064, 1134, 1230, 1670, 1807, 2094, 2369

Offset: 1

Author

M. F. Hasler, Apr 03 2008

Keywords

• nonn

Comments

Can there be an odd multiple of 5 in this sequence?

Links

• Robert Price, Table of n, a(n) for n = 1..110
• Yves Gallot, Cyclotomic polynomials and prime numbers
• Index entries for cyclotomic polynomials, values at X

Crossrefs

Cf. A019323, A138920-A138940.

Programs

Mathematica

Select[Range[1000], PrimeQ[Cyclotomic[#, 5]] &]

PARI

for( i=1,999, ispseudoprime( polcyclo(i,5)) && print1( i","))

Extensions

a(48)-a(54) from Robert Price, Apr 14 2012