A316863 - OEIS

%I #24 Apr 21 2020 13:52:07

%S 0,0,1,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,1,2,1,1,1,1,1,1,1,0,0,1,0,

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

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

%N Number of times 2 appears in the decimal expansion of n.

%H Robert Israel, <a href="/A316863/b316863.txt">Table of n, a(n) for n = 0..10000</a>

%F G.f.: (1-x)^(-1)*Sum_{k>=0} (x^(2*10^k)-x^(3*10^k))/(1-x^(10^(k+1))). - _Robert Israel_, Apr 21 2020

%e a(0) = 0 since the decimal representation of 0 does not contain the digit 2.

%e a(2) = 1 since 2 appears once in the decimal expansion of 2.

%e a(22) = 2 since 2 appears twice in the decimal expansion of 22.

%p f:= n -> numboccur(2,convert(n,base,10)):

%p map(f, [$0..200]); # _Robert Israel_, Apr 21 2020

%t Array[ DigitCount[#, 10, 2] &, 105, 0]

%o (PARI) a(n) = #select(x->x==2, digits(n)); \\ _Michel Marcus_, Jul 20 2018

%Y Cf. A000027, A001477.

%Y Cf. A043497, A043498, A043499, A043500.

%Y Cf. A055641, A268643, A316864, A316865, A316866, A316867, A316868, A316869, A102683.

%K base,easy,nonn

%O 0,23

%A _Robert G. Wilson v_, Jul 15 2018