A257845 a(n) = floor(n/5) * (n mod 5).

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

Offset: 0

Author

M. F. Hasler, May 10 2015

Keywords

• nonn
• easy

Comments

Equivalently, write n in base 5, multiply the last digit by the number with its last digit removed.

Links

• Colin Barker, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,2,0,0,0,0,-1).

Crossrefs

Cf. A142150 (the base 2 analog), A115273, A257844 - A257850.

Programs

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 *)

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

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