login
A047205
Numbers that are congruent to {0, 3, 4} mod 5.
23
0, 3, 4, 5, 8, 9, 10, 13, 14, 15, 18, 19, 20, 23, 24, 25, 28, 29, 30, 33, 34, 35, 38, 39, 40, 43, 44, 45, 48, 49, 50, 53, 54, 55, 58, 59, 60, 63, 64, 65, 68, 69, 70, 73, 74, 75, 78, 79, 80, 83, 84, 85, 88, 89, 90, 93, 94, 95, 98, 99, 100, 103, 104, 105, 108
OFFSET
1,2
FORMULA
G.f.: x^2*(3+x+x^2) / ( (1+x+x^2)*(x-1)^2 ). - R. J. Mathar, Oct 08 2011
From Wesley Ivan Hurt, Jun 14 2016: (Start)
a(n) = a(n-1) + a(n-3) - a(n-4) for n>4.
a(n) = (15*n-9-4*sqrt(3)*sin(2*n*Pi/3))/9.
a(3k) = 5k-1, a(3k-1) = 5k-2, a(3k-2) = 5k-5. (End)
Sum_{n>=2} (-1)^n/a(n) = 3*log(2)/5 - sqrt(1-2/sqrt(5))*Pi/5. - Amiram Eldar, Jan 01 2022
MAPLE
A047205:=n->(15*n-9-4*sqrt(3)*sin(2*n*Pi/3))/9: seq(A047205(n), n=1..100); # Wesley Ivan Hurt, Jun 14 2016
MATHEMATICA
Select[Range[0, 200], MemberQ[{0, 3, 4}, Mod[#, 5]] &] (* Vladimir Joseph Stephan Orlovsky, Feb 12 2012 *)
PROG
(Magma) [ n : n in [0..150] | n mod 5 in [0, 3, 4] ]; // Vincenzo Librandi, Mar 31 2011
(PARI) a(n)=n\3*5+[-1, 0, 3][n%3+1] \\ Charles R Greathouse IV, Dec 22 2011
CROSSREFS
Sequence in context: A173999 A127427 A286994 * A283765 A120631 A047601
KEYWORD
nonn,easy
STATUS
approved