A061352 First row of array shown below.

1, 2, 6, 7, 5, 6, 8, 9, 5, 6, 6, 7, 1, 2, 0, 1, 3, 4, 0, 1, 1, 2, 6, 7, 5, 6, 8, 9, 5, 6, 6, 7, 1, 2, 0, 1, 3, 4, 0, 1, 1, 2, 6, 7, 5, 6, 8, 9, 5, 6, 6, 7, 1, 2, 0, 1, 3, 4, 0, 1, 1, 2, 6, 7, 5, 6, 8, 9, 5, 6, 6, 7, 1, 2, 0, 1, 3, 4, 0, 1, 1, 2, 6, 7, 5, 6, 8, 9, 5, 6, 6, 7, 1, 2, 0, 1, 3, 4, 0, 1, 1, 2, 6, 7, 5

Offset

1,2

Comments

Least significant digit of the n-th triangular number if n is odd.

Links

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

Formula

a(1)=1; if n odd, a(n+1)=(a(n)+1) mod 10; if n even, a(n+1)=(a(n)+2n) mod 10.

a(2n-1) = n*(2n-1)- 10*Floor[n*(2n-1)/10], a(2n) = n(2n+1)- 10*Floor[n*(2n+1)/10] + 1.

Example

1 2 6 7 5 6 8 9 5 ...
3 5 8 4 7 7 0 4 ...
4 9 3 8 6 1 3 ...
0 2 9 5 2 2 ...
1 0 4 3 1 ...
1 3 4 0 ...

Crossrefs

Cf. A061353.

Sequence in context: A377969 A327558 A265180 * A173991 A039926 A242430

Adjacent sequences: A061349 A061350 A061351 * A061353 A061354 A061355

Keyword

nonn,easy

Author

Amarnath Murthy, Apr 28 2001

Extensions

More terms and formula from Larry Reeves (larryr(AT)acm.org), May 15 2001

Status

approved