A138420 a(n) = ((prime(n))^4-(prime(n))^2)/4.

3, 18, 150, 588, 3630, 7098, 20808, 32490, 69828, 176610, 230640, 468198, 706020, 854238, 1219368, 1971918, 3028470, 3460530, 5036658, 6351660, 7098228, 9735960, 11862858, 15683580, 22129968, 26012550, 28135068, 32767038, 35286570

Offset: 1

Author

Artur Jasinski, Mar 19 2008

Keywords

• nonn
• easy

Comments

Number of monic irreducible polynomials of degree 4 over GF(prime(n)). - Robert Israel, Jan 07 2015

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A008837, A127919, A138420, A138426.

Programs

Magma

[(NthPrime((n))^4 - NthPrime((n))^2)/4: n in [1..30] ]; // Vincenzo Librandi, Jun 17 2011

Maple

seq(1/4*(ithprime(i)^4 - ithprime(i)^2), i=1..100); # Robert Israel, Jan 07 2015

Mathematica

a = {}; Do[p = Prime[n]; AppendTo[a, (p^4 - p^2)/4], {n, 1, 50}]; a
(#^4-#^2)/4&/@Prime[Range[30]] (* Harvey P. Dale, Aug 01 2025 *)

PARI

forprime(p=2,1e3,print1((p^4-p^2)/4", ")) \\ Charles R Greathouse IV, Jul 15 2011

Formula

a(n) = A138402(n)/4. - R. J. Mathar, Oct 15 2017

Extensions

Name edited by Robert Israel, Jan 07 2015