OFFSET
1,2
COMMENTS
The next four numbers are 7,8,9 and 10 and hence the next terms are all the numbers formed by the digits 1,0,7,8 and 9 in ascending order.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..5000
EXAMPLE
The next two numbers are 2 and 3 and the two numbers that can be formed are 23 and 32 hence a(2) = 23 and a(3) = 32.
MATHEMATICA
uad[l_]:=Module[{d=Flatten[IntegerDigits/@l], len}, len=Length[d]; Select[FromDigits/@ Permutations[ d], IntegerLength[#]==len&]//Sort]; uad/@With[{nn=4}, TakeList[Range[ (nn(nn+1))/2], Range[nn]]]//Flatten (* Harvey P. Dale, Jan 01 2024 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Apr 05 2003
EXTENSIONS
More terms from David Wasserman, Jul 27 2004
STATUS
approved