A138928 Indices n such that A020501(n) = phi(n)(-2) is prime, where Phi is a cyclotomic polynomial.

3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 24, 26, 30, 31, 32, 34, 38, 39, 40, 43, 45, 49, 54, 56, 61, 62, 63, 66, 75, 79, 80, 85, 87, 98, 101, 117, 120, 122, 127, 130, 138, 154, 161, 167, 170, 178, 183, 184, 186, 187, 191, 192, 199, 205, 207, 208

Offset: 1

Author

M. F. Hasler, Apr 03 2008

Keywords

• nonn

Comments

While the sequence is not very interesting up to a(n)<300, there are only 4 values in the interval [400,599].

Links

• Robert Price, Table of n, a(n) for n = 1..227
• Yves Gallot, Cyclotomic polynomials and prime numbers
• Index entries for cyclotomic polynomials, values at X

Crossrefs

Cf. A020501, A138920-A138940.

Programs

Mathematica

Select[ Range[3, 1000], PrimeQ[ Cyclotomic[#, -2]] &] (* Robert G. Wilson v, Mar 25 2012 *)

PARI

for( i=1,999, isprime( polcyclo(i,-2)) && print1( i",")) /* for PARI < 2.4.2 use ...subst(polcyclo(i),x,-2)...*/