A297152 Positive numbers whose decimal expansion contains a 3-digit substring abc such that b > a > c.

120, 130, 140, 150, 160, 170, 180, 190, 230, 231, 240, 241, 250, 251, 260, 261, 270, 271, 280, 281, 290, 291, 340, 341, 342, 350, 351, 352, 360, 361, 362, 370, 371, 372, 380, 381, 382, 390, 391, 392, 450, 451, 452, 453, 460, 461, 462, 463, 470, 471, 472, 473

Offset

1,1

Comments

The number of n-digit numbers that start with this substring is 12*10^(n-2), n>=3, hence about 12% of n-digit numbers are of this kind, n>=3. None of the numbers that start with this substring begin with 9.

Links

Table of n, a(n) for n=1..52.

Example

The 3-digit numbers with this substring are 120, 130, ..., 190, ... 890, 891, ..., 897 (there are 120 of these).  The next numbers after 879 are 1200, 1201, etc. since they contain the string 120.
There are numbers of any length n, n>=3, that contain this substring, such as *231 or 231** where * is free since the substring 231 is already there.

Crossrefs

Sequence in context: A157425 A030501 A271578 * A074302 A095631 A248662

Adjacent sequences: A297149 A297150 A297151 * A297153 A297154 A297155

Keyword

nonn,base

Author

Enrique Navarrete, Dec 26 2017

Status

approved