A351653 a(n) is the concatenation of the length of each run of digits in the decimal representation of n.
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 11, 2, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 2, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 2, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 2, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 2, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 2, 11, 11
Offset: 0
Examples
a(100) = 12, because the 1st run (1) has length 1 and the 2nd run (00) has length 2. a(13211) = 1112, because the 1st run (1) has length 1, the 2nd run (3) has length 1, the 3rd run (2) has length 1 and the 4th run (11) has length 2.
Programs
-
Mathematica
a[n_] := FromDigits[IntegerDigits[Length /@ Split[IntegerDigits[n]]] // Flatten]; Array[a, 100, 0] (* Amiram Eldar, Feb 16 2022 *)
-
PARI
a(n) = {my(result = "", count = 0, dig = digits(n), last = dig[1]); for(i = 1, length(dig), current = dig[i]; if (current == last, count++, result = concat(result, Str(count)); count = 1); last = current); result = concat(result, Str(count)); return(eval(result))};
-
PARI
apply( {A351653(n,d=digits(n+!n))=d=concat([0,[k|k<-[1..#n=d[^1]-d[^-1]], n[k]], #d]); fromdigits(d[^1]-d[^-1])}, [0..77]) \\ M. F. Hasler, Aug 21 2025
-
Python
from itertools import groupby def A351653(n): return int(''.join(str(len(list(g))) for k, g in groupby(str(n)))) # Chai Wah Wu, Mar 11 2022