A161504 Primes congruent to {1, 2, 10, 11, 19, 20} mod 21.

2, 11, 19, 23, 31, 41, 43, 53, 61, 73, 83, 103, 107, 127, 137, 149, 157, 167, 179, 191, 199, 211, 229, 233, 241, 251, 263, 271, 283, 293, 313, 317, 337, 347, 359, 367, 379, 389, 397, 401, 409, 419, 421, 431, 439, 443, 461, 463, 503, 523, 547, 557, 569, 577, 587

Offset: 1

Author

T. D. Noe, Jun 17 2009

Keywords

• nonn

Comments

The cyclotomic polynomial Phi(21p,x) is flat only for p in this sequence.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1001 [a(1)=2 inserted by _Georg Fischer_, Jul 26 2020]

Crossrefs

Cf. A117223, A124826, A141888, A141892, A141893, A141897, A141898, A160495.

Programs

Mathematica

Flatten[Table[Select[21*n+{-10,-2,-1,1,2,10}, PrimeQ], {n,50}]]
Select[Prime[Range[2,250]],MemberQ[{1,2,10,11,19,20},Mod[#,21]]&] (* Harvey P. Dale, May 03 2019 *)

Formula

Union of A124826, A141888, A141892, A141893, A141897, A141898.

Extensions

a(1)=2 inserted by Georg Fischer, Jul 26 2020