OFFSET
0,2
COMMENTS
a(-2)=2, a(-1)=0. 4 evens followed by 4 odds.
Last digit is only 0, 2, 5, 7.
The vertical spoke S-N of the pentagonal spiral for A004526.
37
37 25 25
36 24 15 15 26
36 24 14 7 8 16 26
35 23 14 7 2 3 8 16 27
35 23 13 6 2 0 0 3 9 17 27
34 22 13 6 1 1 4 9 17 28
34 22 12 5 5 4 10 18 28
33 21 12 11 11 10 18 29
33 21 20 20 19 19 29
32 32 31 31 30 30
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (3,-4,4,-3,1).
FORMULA
a(-1-n) = a(n).
a(2*n) + a(1+2*n) = 2, 22, 62, ... = A273366(n).
Second differences give the sequence of period 4: repeat [3, 3, 2, 2].
From Colin Barker, Feb 14 2020: (Start)
G.f.: x*(2 + x + 2*x^2) / ((1 - x)^3*(1 + x^2)).
a(n) = 3*a(n-1) - 4*a(n-2) + 4*a(n-3) - 3*a(n-4) + a(n-5) for n>4.
(End)
Multiples of 10: 10*(0, 7, 9, 30, 34, ... = A154260).
4*a(n) = A087960(n) +5*n -1 +5*n^2. - R. J. Mathar, Feb 28 2020
MATHEMATICA
CoefficientList[Series[x (2 + x + 2 x^2)/((1 - x)^3*(1 + x^2)), {x, 0, 42}], x] (* Michael De Vlieger, Feb 14 2020 *)
PROG
(PARI) concat(0, Vec(x*(2 + x + 2*x^2) / ((1 - x)^3*(1 + x^2)) + O(x^40))) \\ Colin Barker, Feb 14 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Feb 14 2020
STATUS
approved