A336528 a(1) = 1; a(2) = 2; for n > 2, a(n) is the least number > a(n-1) whose decimal representation is uniquely the concatenation of the decimal representations of two distinct earlier terms.
1, 2, 12, 21, 112, 122, 211, 221, 1112, 1121, 1211, 1222, 2111, 2122, 2212, 2221, 11112, 11122, 11221, 11222, 12211, 12222, 21111, 21122, 22111, 22112, 22211, 22221, 111112, 111121, 111212, 112112, 112121, 112122, 112212, 121111, 121122, 121211, 121222, 122122
Offset: 1
Examples
The first terms, alongside A007931 and the corresponding concatenations, are:
n a(n) A007931 concatenations
-- ---- ------- --------------
1 1 1
2 2 2
11
3 12 12 1|2
4 21 21 2|1
22
111 1|11, 11|1
5 112 112 1|12
121 1|21, 12|1
6 122 122 12|2
7 211 211 21|1
212 2|12, 21|2
8 221 221 2|21
222
1111
9 1112 1112 1|112
10 1121 1121 112|1
Links
- Rémy Sigrist, Table of n, a(n) for n = 1..15616 (terms < 10^15)
- Tej Bade, Kelly Cui, Antoine Labelle, and Deyuan Li, Ulam Sets in New Settings, arXiv:2008.02762 [math.CO], 2020. See also Integers (2020) Vol. 20, #A102.
- Rémy Sigrist, PARI program for A336528
Programs
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PARI
See Links section.
Comments