A166925 Digital root of square of n-th triangular number.

1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9

Offset

1,2

Comments

Period is (1,9,9).

Links

Table of n, a(n) for n=1..87.

Index entries for linear recurrences with constant coefficients, signature (0,0,1).

Formula

G.f.: x*(1+9*x+9*x^2)/(1-x^3). - Bruno Berselli, May 05 2011

a(n) = A010888(A000537(n)). - Michel Marcus, Mar 17 2023

Mathematica

Table[If[(m9 = Mod[(n(n + 1))^2/4, 9]) == 0, 9, m9], {n, 200}]

Prog

(Magma) &cat[[1, 9, 9]: n in [1..29]];  // Bruno Berselli, May 05 2011

Crossrefs

Cf. A000217, A000537, A010888.

Sequence in context: A145280 A144667 A118428 * A178164 A216035 A171487

Adjacent sequences: A166922 A166923 A166924 * A166926 A166927 A166928

Keyword

base,less,easy,nonn

Author

Zak Seidov, Oct 23 2009

Status

approved