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A257846
a(n) = floor(n/6) * (n mod 6).
1
0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 0, 2, 4, 6, 8, 10, 0, 3, 6, 9, 12, 15, 0, 4, 8, 12, 16, 20, 0, 5, 10, 15, 20, 25, 0, 6, 12, 18, 24, 30, 0, 7, 14, 21, 28, 35, 0, 8, 16, 24, 32, 40, 0, 9, 18, 27, 36, 45, 0, 10, 20, 30, 40, 50, 0, 11, 22, 33, 44, 55, 0, 12, 24
OFFSET
0,9
COMMENTS
Equivalently, write n in base 6, multiply the last digit by the number with its last digit removed.
FORMULA
a(n) = 2*a(n-6)-a(n-12). - Colin Barker, May 11 2015
G.f.: x^7*(5*x^4+4*x^3+3*x^2+2*x+1) / ((x-1)^2*(x+1)^2*(x^2-x+1)^2*(x^2+x+1)^2). - Colin Barker, May 11 2015
MATHEMATICA
Table[Floor[n/6]*Mod[n, 6], {n, 120}] (* Michael De Vlieger, May 11 2015 *)
PROG
(PARI) a(n, b=6)=(n=divrem(n, b))[1]*n[2]
(PARI) concat([0, 0, 0, 0, 0, 0, 0], Vec(x^7*(5*x^4+4*x^3+3*x^2+2*x+1) / ((x-1)^2*(x+1)^2*(x^2-x+1)^2*(x^2+x+1)^2) + O(x^100))) \\ Colin Barker, May 11 2015
CROSSREFS
Cf. A142150 (the base 2 analog), A115273, A257844 - A257850.
Sequence in context: A309957 A365459 A220660 * A203572 A195829 A095874
KEYWORD
nonn,easy
AUTHOR
M. F. Hasler, May 10 2015
STATUS
approved