

A216241


Number of nstep walks (each step +1 starting from 0) which are never more than 5 or less than 5.


3



1, 2, 4, 8, 16, 32, 62, 124, 236, 472, 890, 1780, 3340, 6680, 12502, 25004, 46732, 93464, 174554, 349108, 651740, 1303480, 2432918, 4865836, 9080956, 18161912, 33892954, 67785908, 126494956, 252989912, 472095062, 944190124, 1761901676, 3523803352, 6575544410, 13151088820
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OFFSET

0,2


LINKS

Table of n, a(n) for n=0..35.


FORMULA

a(n) = A068913(5,n).
a(n) = 6*a(n2)  9*a(n4) + 2*a(n6).
a(n) = 2^n for n < 6.
G.f.: ((1x)^2*(1+x)^2*(1+2*x)) / ((12*x^2)*(14*x^2+x^4)).
a(2*n+1) = 2*a(2*n).
a(n) = Sum_{k=0..n} A214846(nk, k).  Philippe Deléham, Mar 25 2013


MATHEMATICA

nn=35; CoefficientList[Series[(1+2x)(1x^2)^2/(16x^2+9x^42x^6), {x, 0, nn}], x] (* Geoffrey Critzer, Jan 14 2014 *)


CROSSREFS

Cf. Rows of A068913: A000007, A016116 (without initial term), A068911, A068912, A214846, A216212.
Sequence in context: A274005 A027560 A135493 * A283837 A111663 A054043
Adjacent sequences: A216238 A216239 A216240 * A216242 A216243 A216244


KEYWORD

nonn,walk,easy


AUTHOR

Philippe Deléham, Mar 15 2013


EXTENSIONS

a(34) corrected by Sean A. Irvine, May 19 2019


STATUS

approved



