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A061352
First row of array shown below.
2
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.
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: A365256 A327558 A265180 * A173991 A039926 A242430
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