A103756 Number of contiguous digits i in the counting numbers, for i=2.

1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 2, 5, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1

Offset: 1

Author

Alexandre Wajnberg, Mar 28 2005

Keywords

• nonn
• base

Comments

Write the natural numbers as an infinite sequence of digits, starting at the left; and count the digits of each group of "2"'s you encounter (the smallest "groups" have one "2").

Examples

			a(1)=1: the first "2" of the counting numbers, isolated.
a(2)=1: the second "2", second digit of number 12, isolated.
a(3)=1 the first digit of number 20, isolated.
a(4)=1: the first digit of number 21, isolated.
a(5)=3: two "2"'s of 22 followed by one "2" of 23 = three "2"'s, the next group of "2"'s.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Length/@Select[Split[Flatten[IntegerDigits/@Range[300]]],Union[#]=={2}&] (* Harvey P. Dale, Jun 10 2023 *)