login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A359142 Let s = sum of digits of n, let t = decimal concatenation of n and s, let u be obtained by deleting all copies of the leading digit of t from t, if this digit occurs in s. Then if u has only zero digits, a(n) = 0; if u has leading digit 0 but not all its digits are 0, delete all leading 0's from u and negate the result to get a(n); otherwise a(n) = u. 5
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 112, 123, 134, 145, 156, 167, 178, 189, 90, 0, 213, 224, 235, 246, 257, 268, 279, 2810, 2911, 0, 314, 325, 336, 347, 358, 369, 3710, 3811, 3912, 0, 415, 426, 437, 448, 459, 4610, 4711, 4812, 4913, 0, 516, 527, 538, 549, 5510, 5611, 5712, 5813 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,11
COMMENTS
Since nonzero numbers may not have leading zeros, we indicate their presence by negating the number.
For use in A359142, we also define a(n) for improper decimal numbers n with leading zeros by following exactly the same steps. To get a(073), for example, we append the digit sum 10, and delete the 0's from 07310, getting a(073) = 731. To get a(074), we append 11, getting 07411, so a(074) = -7411.
The sequence of n such that a(n) < 0 begins (109, 1009, 1018, 1019, 1027, 1028, 1029, 1036, ...): see A359144. - M. F. Hasler, Feb 01 2023
LINKS
Eric Angelini, Does this iteration end? (Sum and erase), Personal blog "Cinquante Signes", blogspot.com, Jul 26 2022.
Hans Havermann, Cycles in Eric Angelini's sum-and-erase, Personal blog "Glad Hobo Express", blogspot.com, Jul 28 2022.
N. J. A. Sloane, New Gilbreath Conjectures, Sum and Erase, Dissecting Polygons, and Other New Sequences, Doron Zeilberger's Exper. Math. Seminar, Rutgers, Sep 14 2023: Video, Slides, Updates. (Mentions this sequence.)
EXAMPLE
Examples:
n.....s......t....u.....a(n)
1.....1.....11....0......0
2.....2.....22....0......0
.....
9.....9.....99....0......0
10....1....101....0......0
11....2....112..112....112
12....3....123..123....123
.....
100...1...1001...00......0
101...2...1012.1012...1012
102...3...1023.1023...1023
.....
109..10..10910..090....-90
.....
MATHEMATICA
A359142[n_]:= Module[{d=IntegerDigits[n], s, u}, If[MemberQ[s=IntegerDigits[Total[d]], First[u=Join[d, s]]], u=DeleteCases[u, First[u]]]; If[u=={}||First[u]==0, -1, 1]FromDigits[u]]; Array[A359142, 100] (* Paolo Xausa, Oct 11 2023 *)
PROG
(PARI) A359142(n) = { my(d=digits(n), s=digits(vecsum(d))); n>0 || d=concat(0, d); n=concat(d, s); setsearch(Set(s), d[1]) && n=select(c->c!=d[1], n); if(n && !n[1], -fromdigits(n), fromdigits(n)) }
apply(A359142, [0..99]) \\ M. F. Hasler, Feb 01 2023
(Python)
def a(n):
n = str(-n) if isinstance(n, int) and n < 0 else str(n)
s = str(sum(map(int, n)))
t = n + s
u = t.replace(t[0], "") if t[0] in s else t
return 0 if u == "" else (-int(u) if u[0] == "0" else int(u))
print([a(n) for n in range(1, 59)]) # Michael S. Branicky, Feb 01 2023
CROSSREFS
Cf. A359143, A359144 (k such that a(k)<0).
Sequence in context: A281926 A036301 A117723 * A329719 A157662 A340125
KEYWORD
sign,base
AUTHOR
N. J. A. Sloane, Jan 31 2023, based on suggestions from Eric Angelini and Hans Havermann
EXTENSIONS
More terms from M. F. Hasler, Feb 01 2023
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 19 09:37 EDT 2024. Contains 373501 sequences. (Running on oeis4.)