A396497 Numbers k such that 90*k-1, 120*k-1, 180*k-1, 240*k-1, 360*k-1, 720*k-1 are all primes.

2, 14973, 20736, 22066, 38068, 42504, 56672, 74426, 86387, 87201, 94689, 108794, 109909, 110840, 114732, 148262, 150843, 159306, 220290, 236735, 245366, 246822, 259380, 433162, 474812, 483854, 487258, 500346, 509630, 530586, 677432, 695081, 696775, 724978, 780628

Offset

1,1

Comments

Any occurrence of 4 consecutive numbers in A395563, indices of 2 in A395473, is either (20, 21, 22, 23) or of the form (720*k-4, 720*k-3, 720*k-2, 720*k-1) exactly for k being in this sequence.

Links

Jianing Song, Table of n, a(n) for n = 1..10000

Example

2 is a term since (90*k-1, 120*k-1, 180*k-1, 240*k-1, 360*k-1, 720*k-1) = (179, 239, 359, 479, 719, 1439) are all primes. This corresponds to the 4 consecutive members (1436, 1437, 1438, 1439) in A395563.
14973 is a term since (1347569, 1796759, 2695139, 3593519, 5390279, 10780559) are all primes. This corresponds to the 4 consecutive members (10780556, 10780557, 10780558, 10780559) in A395563.

Prog

(PARI) isA396497(k) = isprime(90*k-1) && isprime(120*k-1) && isprime(180*k-1) && isprime(240*k-1) && isprime(360*k-1) && isprime(720*k-1)

Crossrefs

Cf. A396495 ({90*k-1}), A395473, A395563.

Sequence in context: A151599 A297573 A346566 * A159730 A264944 A242855

Adjacent sequences: A396494 A396495 A396496 * A396498 A396499 A396500

Keyword

nonn

Author

Jianing Song, May 28 2026

Status

approved