A301812 Numbers of the form p^2 - 1 where p is a prime of the form 3*k-1 (A003627).

3, 24, 120, 288, 528, 840, 1680, 2208, 2808, 3480, 5040, 6888, 7920, 10200, 11448, 12768, 17160, 18768, 22200, 27888, 29928, 32040, 36480, 38808, 51528, 54288, 57120, 63000, 66048, 69168, 72360, 78960, 85848, 96720, 100488, 120408, 124608, 128880, 146688

Offset: 1

Author

Peter Luschny, Mar 27 2018

Keywords

• nonn
• easy

Crossrefs

Cf. A003627, A084920.

Programs

Maple

A301812List := proc(len) local p, n, L; L := 3; p := 5;
for n from 2 to len do if isprime(p) then L := L,(p^2 - 1) fi;
p := p + 6; od: L end:
A301812List(65);

Mathematica

Flatten[Table[n^2 - 1, {n, {2, Select[Range[5, 385, 6], PrimeQ]}}]]

Formula

a(n) = A003627(n)^2 - 1. - Altug Alkan, Mar 28 2018