A061352 - OEIS

%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