This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A171225 #5 Apr 25 2016 12:09:17
%S A171225 160,178,196,211,219,221,223,227,229,233,235,237,239,241,247,250,253,
%T A171225 259,274,277,284,286,287,292,295,300,302,304,309,310,312,313,319,325,
%U A171225 331,337,349,363,367,368,372,377,381,382,385,388,390,391,392,395,397,399,400,401
%N A171225 Nonnegative numbers which cannot be represented by inserting plus or minus signs between the digits of 123456789.
%C A171225 a(1)=160 is the smallest number which can't be described by such expressions.
%C A171225 159 has 6 ways to reach it: 159 = 123-45-6+78+9 = 123+4+56-7-8-9 = 1+234+5+6-78-9 = 1+23+45-6+7+89 = 123-4-56+7+89 = 1-2+3-4+5+67+89.
%C A171225 There are 3^8=6561 ways to form expressions of that kind, including duplicates and negative numbers. - _R. J. Mathar_, Dec 07 2009
%o A171225 (Excel) VBA Program:
%o A171225 Sub Test() Dim Solutions(1 To 1000), result As Single Dim temp As Long, x(1 To 17) As String, op Dim i As Long, j As Long, out As String, num As Long op = Array("+", "-", "") For i = 1 To 9 x(2 * i - 1) = i Next For i = 0 To 3 ^ 8 - 1 temp = i For j = 1 To 8 x(2 * j) = op(temp Mod 3) temp = temp \ 3 Next out = Join(x, "") result = Evaluate(out) If result > 0 Then If result < 1001 Then Solutions(result) = Solutions(result) + 1 End If End If Next For i = 1 To 1000 If Solutions(i) = 0 Then Debug.Print i; Next End Sub
%Y A171225 Cf. A066956.
%K A171225 nonn,easy,base
%O A171225 1,1
%A A171225 _Zhining Yang_, Dec 05 2009
%E A171225 Definition rephrased, terms beyond 300 added by _R. J. Mathar_, Dec 07 2009