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A257845 a(n) = floor(n/5) * (n mod 5). 2
0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 0, 2, 4, 6, 8, 0, 3, 6, 9, 12, 0, 4, 8, 12, 16, 0, 5, 10, 15, 20, 0, 6, 12, 18, 24, 0, 7, 14, 21, 28, 0, 8, 16, 24, 32, 0, 9, 18, 27, 36, 0, 10, 20, 30, 40, 0, 11, 22, 33, 44, 0, 12, 24, 36, 48, 0, 13, 26, 39, 52, 0, 14, 28, 42, 56 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,8
COMMENTS
Equivalently, write n in base 5, multiply the last digit by the number with its last digit removed.
LINKS
FORMULA
a(n) = 2*a(n-5)-a(n-10). - Colin Barker, May 11 2015
G.f.: x^6*(4*x^3+3*x^2+2*x+1) / ((x-1)^2*(x^4+x^3+x^2+x+1)^2). - Colin Barker, May 11 2015
MATHEMATICA
LinearRecurrence[{0, 0, 0, 0, 2, 0, 0, 0, 0, -1}, {0, 0, 0, 0, 0, 0, 1, 2, 3, 4}, 80] (* Harvey P. Dale, Aug 15 2021 *)
PROG
(PARI) a(n, b=5)=(n=divrem(n, b))[1]*n[2]
(PARI) concat([0, 0, 0, 0, 0, 0], Vec(x^6*(4*x^3+3*x^2+2*x+1) / ((x-1)^2*(x^4+x^3+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: A082853 A230431 A190886 * A162593 A279125 A011025
KEYWORD
nonn,easy
AUTHOR
M. F. Hasler, May 10 2015
STATUS
approved

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)