|
|
A247840
|
|
Sum(6^k, k=2..n).
|
|
2
|
|
|
0, 36, 252, 1548, 9324, 55980, 335916, 2015532, 12093228, 72559404, 435356460, 2612138796, 15672832812, 94036996908, 564221981484, 3385331888940, 20311991333676, 121871948002092, 731231688012588, 4387390128075564, 26324340768453420
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
FORMULA
|
G.f.: 36*x^2/((1-x)*(1-6*x)).
a(n) = a(n-1) + 6^n = (6^(n+1) - 36)/5 = 7*a(n-1) - 6*a(n-2).
|
|
MATHEMATICA
|
RecurrenceTable[{a[1] == 0, a[n] == a[n-1] + 6^n}, a, {n, 30}] (* or *) CoefficientList[Series[36 x / ((1 - x) (1 - 6 x)), {x, 0, 30}], x]
Join[{0}, Accumulate[6^Range[2, 30]]] (* or *) LinearRecurrence[{7, -6}, {0, 36}, 30] (* Harvey P. Dale, Jun 11 2016 *)
|
|
PROG
|
(Magma) [0] cat [&+[6^k: k in [2..n]]: n in [2..30]]; /* or */ [(6^(n+1)-36)/5: n in [1..30]];
|
|
CROSSREFS
|
Cf. similar sequences listed in A247817.
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|