A321801 Delete all consecutive identical decimal digits of n; write 0 if all digits disappear.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 0, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 0, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 0, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 0, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 0, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 0, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 0, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 0, 1, 101, 102, 103, 104, 105, 106, 107, 108, 109, 0, 0, 2, 3, 4, 5, 6, 7, 8, 9, 120, 121, 1, 123, 124, 125, 126, 127, 128, 129, 130, 131

Offset: 0

Author

Chai Wah Wu, Nov 19 2018

Keywords

• nonn
• base

Comments

Consecutive identical digits of n are erased. Leading zeros are erased unless the result is 0. If all digits are erased, we write 0 for the result (A321802 is another version, which uses -1 for the empty string).

More than the usual number of terms are shown in order to reach some interesting examples. Agrees with A320486 for n < 101.

Examples

			12311 becomes 123, 1123 becomes 23, 11231 becomes 231, and 110232 becomes 232 (as we don't accept leading zeros). Note that 112233 disappears immediately and we get 0.
1110, 11000, 1100011 all become 0.
		

Links

• Paolo Xausa, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A320486, A321802.

Programs

Mathematica

A321801[n_]:=FromDigits[Flatten[Select[Split[IntegerDigits[n]],Length[#]==1&]]];Array[A321801,100,0] (* Paolo Xausa, Nov 14 2023 *)

PARI

A321801(n)={forstep(i=#n=digits(n),2,-1,n[i]!=n[i-1]&&next;if(i<3||n[i-2]!=n[i],n=n[^i];i--);n=n[^i]);fromdigits(n)} \\ M. F. Hasler, Nov 20 2018

Python

from re import split
def A321801(n):
    return int('0'+''.join(d if len(d) == 1 else '' for d in split('(0+)|(1+)|(2+)|(3+)|(4+)|(5+)|(6+)|(7+)|(8+)|(9+)',str(n)) if d != '' and d != None))