|
| |
|
|
A254676
|
|
Heptagonal numbers (A000566) which are also centered triangular numbers (A005448).
|
|
3
|
|
|
|
1, 235, 2839, 902101, 10906669, 3465871039, 41903418691, 13315875628969, 160992923703385, 51159590700627091, 618534770964985711, 196555134155933653885, 2376410429054551397509, 755164774267506397598311, 9130168249892815504243099, 2901342866180625423639056209
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
LINKS
|
|
|
|
FORMULA
|
a(n) = a(n-1)+3842*a(n-2)-3842*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+234*x^3-1238*x^2+234*x+1) / ((x-1)*(x^2-62*x+1)*(x^2+62*x+1)).
|
|
|
EXAMPLE
|
235 is in the sequence because it is the 10th heptagonal number and the 13th centered triangular number.
|
|
|
PROG
|
(PARI) Vec(-x*(x^4+234*x^3-1238*x^2+234*x+1)/((x-1)*(x^2-62*x+1)*(x^2+62*x+1)) + O(x^100))
|
|
|
CROSSREFS
|
|
|
|
KEYWORD
|
nonn,easy
|
|
|
AUTHOR
|
|
|
|
STATUS
|
approved
|
| |
|
|
