A083228 A Jacobsthal related sequence.

1, 3, 21, 341, 10923, 699051, 89478485, 22906492245, 11728124029611, 12009599006321323, 24595658764946068821, 100743818301219097892181, 825293359523586849932749483, 13521606402434446949298167524011

Offset: 0

Author

Paul Barry, Apr 23 2003

Keywords

• easy
• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..55

Crossrefs

Cf. A000217.

Programs

Magma

[2^Binomial(n+2, 2)/3-(-1)^Binomial(n+2, 2)/3: n in [0..15]]; // Vincenzo Librandi, Jun 29 2011

PARI

a(n)=2^binomial(n+2, 2)\/3 \\ Charles R Greathouse IV, Jun 29 2011

Formula

a(n) = A001045(binomial(n+2, 2)) = 2^binomial(n+2, 2)/3 - (-1)^binomial(n+2, 2)/3.