A161504 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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]

FORMULA

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

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 *)