A130686 Absolute difference of final digits of two consecutive triangular numbers.

1, 2, 3, 6, 5, 4, 7, 2, 1, 0, 1, 2, 7, 4, 5, 6, 3, 2, 1, 0, 1, 2, 3, 6, 5, 4, 7, 2, 1, 0, 1, 2, 7, 4, 5, 6, 3, 2, 1, 0, 1, 2, 3, 6, 5, 4, 7, 2, 1, 0, 1, 2, 7, 4, 5, 6, 3, 2, 1, 0, 1, 2, 3, 6, 5, 4, 7, 2, 1, 0, 1, 2, 7, 4, 5, 6, 3, 2, 1, 0, 1, 2, 3, 6, 5, 4, 7, 2, 1, 0, 1, 2, 7, 4, 5, 6, 3, 2, 1, 0, 1, 2, 3, 6, 5

Offset: 1

Author

Giovanni Teofilatto, Jun 30 2007

Keywords

• base
• easy
• nonn

Comments

Periodic with period 20.

Links

• Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1).

Crossrefs

Cf. A008954.

Programs

Maple

A000217 := proc(n) n*(n+1)/2 ; end: A010879 := proc(n) n mod 10 ; end: A130686 := proc(n) abs(A010879(A000217(n+1))-A010879(A000217(n))) ; end: seq(A130686(n),n=0..80) ; # R. J. Mathar, Jul 15 2007

Formula

a(n) = abs{ A010879[A000217(n+1)] - A010879[A000217(n)] }. - R. J. Mathar, Jul 15 2007