The Pell sequence is named after the English mathematician John Pell. It is formed recursively with the formula

or as a closed formula

The first numbers are

0,

1,

2,

5,

12,

29,

70,

169,

408,

985,

2378,

5741,

13860,

33461,

80782,

195025,

470832,

1136689,

2744210,

6625109,

15994428,

38613965,

93222358,

225058681,

543339720,

1311738121,

3166815962,

7645370045,

18457556052,

44560482149,

107578520350,

259717522849