A043508 -id:A043508 - cp's OEIS frontend

A316865 Number of times 4 appears in decimal expansion of n.

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, 0, 0, 0, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 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, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1

Offset: 0

Robert G. Wilson v, Jul 15 2018

			a(0) = 0 since the decimal representation of 0 does not contain the digit 4.
a(4) = 1 since 4 appears once in the decimal expansion of 4.

Cf. A043505, A043506, A043507, A043508.

Cf. A055641, A268643, A316863, A316864, A316866, A316867, A316868, A316869, A102683.

Mathematica
```
Array[ DigitCount[#, 10, 4] &, 105, 0]
```

a(n) = #select(x->x==4, digits(n)); \\ Michel Marcus, Jul 20 2018

A259528 n-th number with exactly n n's in base 10.

Original entry on oeis.org

1, 122, 2333, 34444, 455555, 5666666, 67777777, 788888888, 8999999999, 101010101010101010010, 11111111110111111111111, 1212121121212121212121212, 131313013131313131313131313, 14141241414141414141414141414

Offset: 1

Jonathan Vos Post, Jun 29 2015

Main diagonal M[n,n,n] of M[i,j,k] = k-th natural number such that number of i's in base 10 is j, for i,j,k = 1,2,3,4,5,....
M[1,1,n] = A043493 Numbers that contain a single 1.
M[2,2,n] = A043498 Numbers n such that number of 2's in base 10 is 2.
M[3,3,n] = A043503 Numbers n such that number of 3's in base 10 is 3.
M[4,4,n] = A043508 Numbers n such that number of 4's in base 10 is 4.

			First element is 1, the 1st natural number with exactly one 1 in base 10.
Second element is 122, the 2nd natural number with exactly two 2's in base 10.
Third element is 2333, the 3rd natural number with exactly three 3's in base 10.

Cf. A043493, A043498, A043503, A043508.

a(n)=my(v=List(),k=10^#Str(n),d=List(digits((k^n-1)/(k-1)*n)),t); for(i=1,#d+1, t=d; listinsert(t,0,i); t=Vec(t); for(j=0,9, t[i]=j; listput(v,fromdigits(t)))); Set(v)[n] \\ Charles R Greathouse IV, Jun 29 2015

a(5)-a(14) from Charles R Greathouse IV, Jun 29 2015

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A316865 Number of times 4 appears in decimal expansion of n.

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