login
Number of 7's in decimal expansion of triangular number n(n+1)/2.
10

%I #11 May 05 2024 19:32:07

%S 0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,1,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,

%T 0,0,0,1,1,1,0,0,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,1,2,0,0,0,0,0,0,0,1,

%U 0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,1,0,1,0,0,0,0,0,1,1,0,0,0,1,0,0,0,0,0,0,0

%N Number of 7's in decimal expansion of triangular number n(n+1)/2.

%H Paolo Xausa, <a href="/A086078/b086078.txt">Table of n, a(n) for n = 0..10000</a>

%t DigitCount[Accumulate[Range[0, 100]], 10, 7] (* _Paolo Xausa_, May 05 2024 *)

%Y Cf. 0's A086071, 1's A086072, 2's A086073, 3's A086074, 4's A086075, 5's A086076, 6's A086077, 8's A086079, 9's A086080.

%Y Cf. A000217.

%K base,nonn

%O 0,60

%A _Jason Earls_, Jul 08 2003