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A047620
Numbers that are congruent to {0, 1, 2, 5} mod 8.
2
0, 1, 2, 5, 8, 9, 10, 13, 16, 17, 18, 21, 24, 25, 26, 29, 32, 33, 34, 37, 40, 41, 42, 45, 48, 49, 50, 53, 56, 57, 58, 61, 64, 65, 66, 69, 72, 73, 74, 77, 80, 81, 82, 85, 88, 89, 90, 93, 96, 97, 98, 101, 104, 105, 106, 109, 112, 113, 114, 117, 120, 121, 122
OFFSET
1,3
FORMULA
From R. J. Mathar, Oct 08 2011: (Start)
G.f.: x^2*(1+3*x^2) / ( (x^2+1)*(x-1)^2 ).
a(n) = 2*n-3+sin(n*Pi/2). (End)
From Wesley Ivan Hurt, May 22 2016: (Start)
a(n) = 2*a(n-1) - 2*a(n-2) + 2*a(n-3) - a(n-4) for n>4.
a(n) = (4n-6+I^(1-n)-I^(1+n))/2 where i=sqrt(-1).
a(2n+2) = A016813(n) n>0, a(2n-1) = A047467(n). (End)
Sum_{n>=2} (-1)^n/a(n) = Pi/16 + 5*log(2)/8. - Amiram Eldar, Dec 19 2021
MAPLE
A047620:=n->(4*n-6+I^(1-n)-I^(1+n))/2: seq(A047620(n), n=1..100); # Wesley Ivan Hurt, May 22 2016
MATHEMATICA
Table[(4n-6+I^(1-n)-I^(1+n))/2, {n, 80}] (* Wesley Ivan Hurt, May 22 2016 *)
LinearRecurrence[{2, -2, 2, -1}, {0, 1, 2, 5}, 120] (* Harvey P. Dale, Mar 11 2017 *)
PROG
(Sage) [lucas_number1(n, 0, 1)+2*n-3 for n in range(1, 57)] # Zerinvary Lajos, Jul 06 2008
(Magma) [n : n in [0..150] | n mod 8 in [0, 1, 2, 5]]; // Wesley Ivan Hurt, May 22 2016
KEYWORD
nonn,easy
EXTENSIONS
More terms from Wesley Ivan Hurt, May 22 2016
STATUS
approved