OFFSET
1,2
COMMENTS
Numbers that are congruent to {1, 4, 5, 7, 8, 11} mod 12. - Amiram Eldar, Jan 24 2023
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Index entries for linear recurrences with constant coefficients, signature (2,-1,-1,2,-1).
FORMULA
Sum_{n>=1} (-1)^(n+1)/a(n) = (1-1/(4*sqrt(3)))*Pi/3. - Amiram Eldar, Jan 24 2023
From Stefano Spezia, Jul 10 2024: (Start)
G.f.: x*(1 + 2*x - 2*x^2 + 2*x^3 + x^4)/((1 - x)^2*(1 + x^3)).
MATHEMATICA
Select[Range[140], Mod[#, 3] > 0 && Mod[#, 4] != 2 &] (* Amiram Eldar, Dec 31 2022 *)
PROG
(PARI) isA359380(n) = A187074(n);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Antti Karttunen, Dec 31 2022
STATUS
approved