A024051 a(n) = 5^n - n^2.

1, 4, 21, 116, 609, 3100, 15589, 78076, 390561, 1953044, 9765525, 48828004, 244140481, 1220702956, 6103515429, 30517577900, 152587890369, 762939452836, 3814697265301, 19073486327764, 95367431640225

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..300
• Index entries for linear recurrences with constant coefficients, signature (8, -18, 16, -5).

Programs

Magma

[5^n-n^2: n in [0..35]]; // Vincenzo Librandi, Jun 12 2011

Mathematica

Table[5^n-n^2,{n,0,20}] (* or *) LinearRecurrence[{8,-18,16,-5},{1,4,21,116},30] (* Harvey P. Dale, Nov 22 2012 *)

Formula

a(n) = 8*a(n-1) - 18*a(n-2) + 16*a(n-3) - 5*a(n-4).