OFFSET
0,2
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1).
FORMULA
a(n) = 9*n^2-1 for n>0 and even.
a(n) = (9*n^2-1)/2 for n odd.
a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6) for n>6.
G.f.: (1+4*x+32*x^2+28*x^3+41*x^4+4*x^5-2*x^6) / ((1-x)^3*(1+x)^3).
MATHEMATICA
Table[LCM@@{3n+1, 3n-1}, {n, 0, 50}] (* or *) LinearRecurrence[{0, 3, 0, -3, 0, 1}, {1, 4, 35, 40, 143, 112, 323}, 60] (* Harvey P. Dale, Sep 05 2020 *)
PROG
(PARI) vector(60, n, n--; lcm(3*n+1, 3*n-1))
(PARI) Vec((1+4*x+32*x^2+28*x^3+41*x^4+4*x^5-2*x^6) / ((1-x)^3*(1+x)^3) + O(x^60))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 11 2017
STATUS
approved