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A056547 a(n) = 6*n*a(n-1) + 1 with a(0)=1. 5
1, 7, 85, 1531, 36745, 1102351, 39684637, 1666754755, 80004228241, 4320228325015, 259213699500901, 17108104167059467, 1231783500028281625, 96079113002205966751, 8070645492185301207085, 726358094296677108637651 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..15.

FORMULA

a(n) = floor(e^(1/6)*6^n*n!).

a(n) = n!*Sum_{k=0..n} 6^(n-k)/k!. E.g.f.: exp(x)/(1 - 6*x). - Philippe Deléham, Mar 14 2004

From Peter Bala, Mar 01 2017: (Start)

a(n) = Integral_{x = 0..inf} (6*x + 1)^n*exp(-x) dx.

The e.g.f. y = exp(x)/(1 - 6*x) satisfies the differential equation (1 - 6*x)*y' = (7 - 6*x)*y.

a(n) = (6*n + 1)*a(n-1) - 6*(n - 1)*a(n-2).

The sequence b(n) := 6^n*n! also satisfies the same recurrence with b(0) = 1, b(1) = 6. This leads to the continued fraction representation a(n) = 6^n*n!*( 1 + 1/(6 - 6/(13 - 12/(19 - ... - (6*n - 6)/(6*n + 1) )))) for n >= 2. Taking the limit gives the continued fraction representation exp(1/6) = 1 + 1/(6 - 6/(13 - 12/(19 - ... - (6*n - 6)/((6*n + 1) - ... )))). Cf. A010844. (End)

EXAMPLE

a(2) = 6*2*a(1) + 1 = 12*7 + 1 = 85.

CROSSREFS

Cf. A000522, A010844, A010845, A056545, A056546 for analogs. A056547/(A000142*A000400) is an increasingly good approximation to 6th root of e.

Sequence in context: A317353 A302565 A049412 * A293055 A121020 A060237

Adjacent sequences:  A056544 A056545 A056546 * A056548 A056549 A056550

KEYWORD

nonn,easy

AUTHOR

Henry Bottomley, Jun 20 2000

EXTENSIONS

More terms from James A. Sellers, Jul 04 2000

STATUS

approved

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Last modified August 11 06:25 EDT 2020. Contains 336422 sequences. (Running on oeis4.)