OFFSET
0,3
LINKS
FORMULA
a(n) = Product_{k=1..n} ((-3)^k - 1)/(-3 - 1).
a(1) = 1, a(n) = ((-3)^n - 1)*a(n-1)/(-4). - Vincenzo Librandi, Oct 26 2012
a(n) ~ (-1)^floor(n/2) * c * 3^(n*(n+1)/2) / 4^n, where c = Product_{k>=1} (1 - 1/(-3)^k) = 1.2176479365615020492... . - Amiram Eldar, Aug 09 2025
MATHEMATICA
RecurrenceTable[{a[1]==1, a[n]==(((-3)^n - 1) * a[n-1])/(-4)}, a, {n, 18}] (* Vincenzo Librandi, Oct 26 2012 *)
PROG
(Magma) [n le 1 select 1 else ((-3)^n - 1)*Self(n-1)/(-4): n in [1..18]]; // Vincenzo Librandi, Oct 26 2012
CROSSREFS
KEYWORD
sign,easy
AUTHOR
EXTENSIONS
a(0)=1 prepended by Seiichi Manyama, May 30 2025
STATUS
approved
