OFFSET
1,1
COMMENTS
Also, numbers congruent to 12, 18, 22 or 28 (mod 30). Also, numbers such that A056619(n) = 5.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,0,0,1,-1).
FORMULA
a(n+4) = a(n)+30.
From Colin Barker, Feb 12 2018: (Start)
G.f.: 2*x*(2 + x)*(3 + x^2 + x^3) / ((1 - x)^2*(1 + x)*(1 + x^2)).
a(n) = a(n-1) + a(n-4) - a(n-5) for n>5.
(End)
a(n) = (5 + 30*n - 3*(-1)^n + 10*A057077(n))/4. - Stefano Spezia, Dec 26 2021
MATHEMATICA
Select[Range@ 524, MemberQ[{12, 18, 22, 28}, Mod[#, 30]] &] (* Michael De Vlieger, Feb 21 2017 *)
LinearRecurrence[{1, 0, 0, 1, -1}, {12, 18, 22, 28, 42}, 80] (* Harvey P. Dale, Nov 09 2017 *)
PROG
(PARI) a(n)=[12, 18, 22, 28][(n-1)%4+1]+(n-1)\4*30
(PARI) Vec(2*x*(2 + x)*(3 + x^2 + x^3) / ((1 - x)^2*(1 + x)*(1 + x^2)) + O(x^60)) \\ Colin Barker, Feb 12 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
M. F. Hasler, Feb 21 2017
STATUS
approved