|
|
A129889
|
|
Write down n, then n*(n+1).
|
|
3
|
|
|
0, 0, 1, 2, 2, 6, 3, 12, 4, 20, 5, 30, 6, 42, 7, 56, 8, 72, 9, 90, 10, 110, 11, 132, 12, 156, 13, 182, 14, 210, 15, 240, 16, 272, 17, 306, 18, 342, 19, 380, 20, 420, 21, 462, 22, 506, 23, 552, 24, 600, 25, 650, 26, 702, 27, 756, 28, 812, 29, 870, 30, 930, 31, 992, 32, 1056, 33
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,4
|
|
LINKS
|
|
|
FORMULA
|
G.f.: x^2*(1+2*x-x^2)/(1-x^2)^3.
a(n) = ((1+2*n-n^2)*(-1)^n -(1-2*n-n^2))/8.
a(n) = a(n-2) + A124625(n) for n>1. (End)
|
|
MAPLE
|
f:=n-> if n mod 2 = 0 then n/2 else (n^2-1)/4; fi;
|
|
MATHEMATICA
|
Flatten[Table[{n, n(n+1)}, {n, 0, 40}]] (* Harvey P. Dale, Jun 21 2015 *)
|
|
PROG
|
(Magma) [IsEven(n) select n/2 else (n^2-1)/4: n in [0..66]]; // Bruno Berselli, May 06 2011
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|