OEIS A276225 - Implementation in D

a(n+3) = 2*a(n+2) + a(n+1) + a(n) with a(0)=3, a(1)=2, a(2)=6.

Source code

Recurrence with function in string form...

import std.stdio;
import std.range;

void main() {
    "\nOEIS - A276225\n".writeln;
    
    auto a276225Rec(uint n) => recurrence!("2*a[n-1] + a[n-2] + a[n-3]")(3uL, 2uL, 6uL).take(n+1);
    
    writefln("%3s %14s", "n", "a(n)");
    
    foreach(index, sequence; enumerate(a276225Rec(32)))
    {
        writefln("%3d %14d", index, sequence);
    }
    
    writeln;
    a276225Rec(32).writeln;
}

Output

OEIS - A276225

  n           a(n)
  0              3
  1              2
  2              6
  3             17
  4             42
  5            107
  6            273
  7            695
  8           1770
  9           4508
 10          11481
 11          29240
 12          74469
 13         189659
 14         483027
 15        1230182
 16        3133050
 17        7979309
 18       20321850
 19       51756059
 20      131813277
 21      335704463
 22      854978262
 23     2177474264
 24     5545631253
 25    14123715032
 26    35970535581
 27    91610417447
 28   233315085507
 29   594211124042
 30  1513347751038
 31  3854221711625
 32  9816002298330

[3, 2, 6, 17, 42, 107, 273, 695, 1770, 4508, 11481, 29240, 74469, 189659, 483027, 1230182, 3133050, 7979309, 20321850, 51756059, 131813277, 335704463, 854978262, 2177474264, 5545631253, 14123715032, 35970535581, 91610417447, 233315085507, 594211124042, 1513347751038, 3854221711625, 9816002298330]