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%I #2 Dec 05 2013 19:54:50
%S 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,
%T 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,
%U 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
%N First row of array shown below.
%C Least significant digit of the n-th triangular number if n is odd.
%F 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.
%F a(2n-1) = n*(2n-1)- 10*Floor[n*(2n-1)/10], a(2n) = n(2n+1)- 10*Floor[n*(2n+1)/10] + 1.
%e 1 2 6 7 5 6 8 9 5 ...
%e 3 5 8 4 7 7 0 4 ...
%e 4 9 3 8 6 1 3 ...
%e 0 2 9 5 2 2 ...
%e 1 0 4 3 1 ...
%e 1 3 4 0 ...
%Y Cf. A061353.
%K nonn,easy
%O 1,2
%A _Amarnath Murthy_, Apr 28 2001
%E More terms and formula from Larry Reeves (larryr(AT)acm.org), May 15 2001