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

1,2

Comments

Periodic with period 20.

Links

Table of n, a(n) for n=1..105.

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).

Formula

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

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

Crossrefs

Cf. A008954.

Sequence in context: A299207 A277330 A072298 * A213927 A222241 A056023

Adjacent sequences: A130683 A130684 A130685 * A130687 A130688 A130689

Keyword

base,easy,nonn

Author

Giovanni Teofilatto, Jun 30 2007

Status

approved