|
|
A294315
|
|
a(n) = 3*n^3 + n^2.
|
|
1
|
|
|
0, 4, 28, 90, 208, 400, 684, 1078, 1600, 2268, 3100, 4114, 5328, 6760, 8428, 10350, 12544, 15028, 17820, 20938, 24400, 28224, 32428, 37030, 42048, 47500, 53404, 59778, 66640, 74008, 81900, 90334, 99328, 108900, 119068, 129850, 141264, 153328, 166060, 179478
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
All terms are even.
|
|
LINKS
|
|
|
FORMULA
|
a(n) = 3*n^3 + n^2.
G.f.: 2*x*(2 + 6*x + x^2) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>3.
(End)
Sum_{n>=1} 1/a(n) = Pi^2/6 + sqrt(3)*Pi/2 + 9*log(3)/2 - 9.
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi^2/12 - sqrt(3)*Pi - 6*log(2) + 9. (End)
|
|
EXAMPLE
|
a(3)=90 because 3*3^3 + 3^2 = 3*27 + 9 = 90.
|
|
MATHEMATICA
|
Array[3 #^3 + #^2 &, 40, 0] (* or *)
LinearRecurrence[{4, -6, 4, -1}, {0, 4, 28, 90}, 40] (* or *)
CoefficientList[Series[2 x (2 + 6 x + x^2)/(1 - x)^4, {x, 0, 39}], x] (* Michael De Vlieger, Dec 12 2017 *)
|
|
PROG
|
(PARI) a(n) = 3*n^3 + n^2;
(PARI) concat(0, Vec(2*x*(2 + 6*x + x^2) / (1 - x)^4 + O(x^40))) \\ Colin Barker, Dec 11 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|