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A282284
Least common multiple of 3*n+1 and 3*n-1.
3
1, 4, 35, 40, 143, 112, 323, 220, 575, 364, 899, 544, 1295, 760, 1763, 1012, 2303, 1300, 2915, 1624, 3599, 1984, 4355, 2380, 5183, 2812, 6083, 3280, 7055, 3784, 8099, 4324, 9215, 4900, 10403, 5512, 11663, 6160, 12995, 6844, 14399, 7564, 15875, 8320, 17423
OFFSET
0,2
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