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A008953 a(n) is the leading digit of the n-th triangular number, n(n+1)/2. 3

%I

%S 1,3,6,1,1,2,2,3,4,5,6,7,9,1,1,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,

%T 6,6,7,7,7,8,8,9,9,9,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,

%U 2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4

%N a(n) is the leading digit of the n-th triangular number, n(n+1)/2.

%H R. Zumkeller, <a href="/A008953/b008953.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A000030(A000217(n)). - _Reinhard Zumkeller_, May 12 2010]

%o (PARI) a(n) = digits(n*(n+1)/2)[1]; \\ _Michel Marcus_, Jun 20 2018

%Y Cf. A008954. - _Reinhard Zumkeller_, May 12 2010

%K nonn,base

%O 1,2

%A _N. J. A. Sloane_

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Last modified February 21 06:40 EST 2019. Contains 320371 sequences. (Running on oeis4.)