|
|
A257970
|
|
a(1) = 1, a(2) = 2, a(3) = 5; thereafter a(n) = 2 * Sum_{k=1..n-1} a(k).
|
|
3
|
|
|
1, 2, 5, 16, 48, 144, 432, 1296, 3888, 11664, 34992, 104976, 314928, 944784, 2834352, 8503056, 25509168, 76527504, 229582512, 688747536, 2066242608, 6198727824, 18596183472, 55788550416, 167365651248, 502096953744, 1506290861232, 4518872583696, 13556617751088
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
FORMULA
|
a(n) = 3*a(n-1) for n>=5.
a(n) = 16*3^(n-4) for n>=4.
|
|
MATHEMATICA
|
CoefficientList[Series[(x + 1) (x - 1)^2/(1 - 3 x), {x, 0, 33}], x] (* Vincenzo Librandi, May 25 2015 *)
Join[{1, 2, 5}, NestList[3#&, 16, 30]] (* Harvey P. Dale, Dec 20 2018 *)
|
|
PROG
|
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy,less
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|