OFFSET
1,3
COMMENTS
Partial sums of A000975(n-1).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Mircea Merca, Inequalities and Identities Involving Sums of Integer Functions J. Integer Sequences, Vol. 14 (2011), Article 11.9.1.
Index entries for linear recurrences with constant coefficients, signature (3,-1,-3,2).
FORMULA
a(n) = A011377(n-1) for n >= 1. - Joerg Arndt, Apr 22 2016
a(n) = round((8*2^n - 6*n - 9)/12).
a(n) = floor((4*2^n - 3*n - 4)/6).
a(n) = ceiling((4*2^n - 3*n - 5)/6).
a(n) = round((4*2^n - 3*n - 4)/6).
a(n) = a(n-2) + 2^(n-1) - 1, n > 2.
From Bruno Berselli, Jan 15 2011: (Start)
a(n) = (8*2^n - 6*n - 9 + (-1)^n)/12.
G.f.: x^2/((1+x)*(1-2*x)*(1-x)^2). (End)
G.f.: Q(0)/(3*(1-x)^2), where Q(k) = 1 - 1/(4^k - 2*x*16^k/(2*x*4^k - 1/(1 + 1/(2*4^k - 8*x*16^k/(4*x*4^k + 1/Q(k+1)))))); (continued fraction). - Sergei N. Gladkovskii, May 21 2013
a(n) = 2*a(n-1) + floor(n/2) for n > 1. - Bruno Berselli, Apr 30 2014
a(n) = floor(2^(n+1)/3) - floor((n+1)/2). - Seiichi Manyama, Dec 22 2023
EXAMPLE
a(5) = 0 + 1 + 2 + 5 + 10 = 18.
MAPLE
seq(round((4*2^n-3*n-4)/6), n=1..50)
MATHEMATICA
f[n_] := Floor[(4 2^n - 3 n - 4)/6]; f[Range[60]] (* Vladimir Joseph Stephan Orlovsky, Jan 29 2011 *)
CoefficientList[Series[x / ((1 + x) (1 - 2 x) (1 - x)^2), {x, 0, 50}], x] (* Vincenzo Librandi, Mar 26 2014 *)
LinearRecurrence[{3, -1, -3, 2}, {0, 1, 3, 8}, 40] (* or *) Accumulate[ Table[ Floor[ 2^n/3], {n, 40}]] (* Harvey P. Dale, Dec 24 2015 *)
PROG
(Magma) [Floor((4*2^n-3*n-4)/6): n in [1..30]]; // Vincenzo Librandi, Jun 23 2011
(PARI) a(n)=(4<<n-3*n-4)\6 \\ Charles R Greathouse IV, Jul 31 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Mircea Merca, Dec 21 2010
STATUS
approved