A290951 Positive integers with digits in decreasing order that differ by 2.

1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 31, 42, 53, 64, 75, 86, 97, 420, 531, 642, 753, 864, 975, 6420, 7531, 8642, 9753, 86420, 97531

Offset

1,2

Comments

There are 12 - 2*k terms of the sequence with k digits, 1 <= k <= 6.

Links

Table of n, a(n) for n=1..29.

Formula

The terms can be described by the following linear equations:

for 1 <= n <= 9, a(n) = n;

for 10 <= n <= 17, a(n) = 11*(n - 9) + 9;

for 18 <= n <= 23, a(n) = 111*(n - 17) + 309;

for 24 <= n <= 27, a(n) = 1111*(n - 23) + 5309;

for 28 <= n <= 29, a(n) = 11111*(n - 27) + 75309.

Mathematica

Select[Range[10^5], Or[Length@ # == 1, Union@ Differences@ # == {-2}] &@ IntegerDigits@ # &] (* Michael De Vlieger, Aug 15 2017 *)

Crossrefs

Sequence in context: A276822 A326106 A180412 * A114800 A079170 A330927

Adjacent sequences: A290948 A290949 A290950 * A290952 A290953 A290954

Keyword

nonn,base,fini,full

Author

Enrique Navarrete, Aug 14 2017

Status

approved