A337864 a(n) is the number formed by removing from n each digit if it is a duplicate of the previous digit, from left to right.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 2, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 3, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 4, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 5, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 6, 67, 68, 69, 70, 71, 72, 73, 74

Offset: 0

Author

Rodolfo Kurchan, Sep 27 2020

Keywords

• base
• nonn
• easy

Comments

Please see discussion in A337857.

Similar to A137564 from which first differs at a(101) = 101 here, there a(101) = 10.

Differs from A106612 starting at n=100. - R. J. Mathar, Oct 08 2020

Examples

			a(100) = 10. Note that the second zero from the index n = 100 has been removed.
a(101) = 101.
a(1211323171) = 121323171. Note that the third "1" from the index n has been removed.
		

Links

• Michael S. Branicky, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A043096 (fixed points a(n)=n).

Cf. A137564, A337857.

Cf. A090079 (in binary).

Programs

PARI

a(n) = if(n < 10, return(n)); if(n%10 == (n\10)%10, return(a(n\10)), return(a(n\10)*10+n%10)) \\ David A. Corneth, Jul 23 2022

Perl

sub a {my($n)=@; $n =~ s/(.)\1+/$1/g; $n} # _Kevin Ryde, Oct 04 2020

Python

from itertools import groupby
def a(n): return int("".join(k for k, g in groupby(str(n))))
print([a(n) for n in range(75)]) # Michael S. Branicky, Jul 23 2022