%I #20 Oct 22 2022 01:57:08
%S 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,
%T 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,
%U 50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,112,113,114,115,116,117,118,119,120,121
%N Numbers such that digits occur at most twice in decimal representation.
%C a(n) = n for n <= 110; a(111) = 112.
%C Sequence is finite; last term is 99887766554433221100. There are approximately 10^15 terms in total. - _Charles R Greathouse IV_, Oct 20 2022
%C There are < 141709756697784 terms. - _Michael S. Branicky_, Oct 21 2022
%H Reinhard Zumkeller, <a href="/A262530/b262530.txt">Table of n, a(n) for n = 1..91953</a>, all terms <= 10^5
%t nonDigRepQ[n_] := Max[{Take[Flatten[Tally[IntegerDigits[n]]], {2, -1, 2}]}] < 3; Select[Range[1111], nonDigRepQ[#] &] (* _Ivan N. Ianakiev_, Sep 25 2015 *)
%o (Haskell)
%o import Data.List (delete)
%o a262530 n = a262530_list !! (n-1)
%o a262530_list = filter f [1..] where
%o f = g d10' . show where
%o g _ [] = True
%o g ts (d:ds) = elem d ts && g (delete d ts) ds
%o d10' = d10 ++ d10; d10 = "0123456789"
%o (PARI) isok(n) = {my(v = vecsort(digits(n))); my(d = -1); for(i=1, #v, if (v[i] == d, rl++; if (rl > 2, return (0)); , d = v[i]; rl = 1);); return (1);} \\ _Michel Marcus_, Sep 29 2015
%o (PARI) is(n)=my(d=vecsort(digits(n))); for(i=3,#d, if(d[i]==d[i-2], return(0))); 1 \\ _Charles R Greathouse IV_, Oct 20 2022
%o (Python)
%o from math import factorial
%o from itertools import islice
%o from sympy.utilities.iterables import multiset_combinations as mc
%o from sympy.utilities.iterables import multiset_permutations as mp
%o def agen():
%o yield from range(1, 100)
%o for digits in range(3, 21):
%o for f in "123456789":
%o r = "".join(sorted([f]+[d*2 for d in "0123456789" if d != f]))
%o s = set()
%o for c in mc(r, digits-1):
%o for p in mp(c):
%o s.add(int(f + "".join(p)))
%o yield from sorted(s)
%o print(list(islice(agen(), 120))) # _Michael S. Branicky_, Oct 21 2022
%Y Cf. A010784.
%K nonn,base,fini
%O 1,2
%A _Reinhard Zumkeller_, Sep 24 2015