A043638 Numbers whose base-10 representation has exactly 2 runs.

10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 100, 110, 112, 113, 114, 115, 116, 117, 118, 119, 122, 133, 144, 155, 166, 177, 188, 199, 200

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base
• easy

Comments

Coincides with sequence "Number of runs in the base 10 representation of n is even" until reaching 1234.

From Robert Israel, Sep 26 2016: (Start)

Numbers of the form (a*(10^i-10^j) + b*(10^j-1))/9 for some i > j >= 0, a <> b with 1 <= a <= 9, 0 <= b <= 9.

There are 81*(d-1) terms with d digits for each d >= 2. (End)

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A023752.

Programs

Maple

sort([seq(seq(seq(seq((a*(10^i-10^j)+b*(10^j-1))/9, a={$1..9} minus {b}),b=0..9),j=1..i-1),i=2..4)]); # Robert Israel, Sep 26 2016