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.
Select[Range[800],Total[Times@@@Partition[Riffle[IntegerDigits[#],{1,-1},{1,-1,2}],2]]==7&] (* Harvey P. Dale, May 01 2022 *)
Do[ a = IntegerDigits[ n ]; l = Length[ a ]; e = o = {}; Do[ o = Append[ o, a[ [ 2k - 1 ] ] ], {k, 1, l/2 + .5} ]; Do[ e = Append[ e, a[ [ 2k ] ] ], {k, 1, l/2} ]; If[ Abs[ Apply[ Plus, o ] - Apply[ Plus, e ] ] == 2, Print[ n ] ], {n, 1, 1000} ]
Do[ a = IntegerDigits[ n ]; l = Length[ a ]; e = o = {}; Do[ o = Append[ o, a[ [ 2k - 1 ] ] ], {k, 1, l/2 + .5} ]; Do[ e = Append[ e, a[ [ 2k ] ] ], {k, 1, l/2} ]; If[ Abs[ Apply[ Plus, o ] - Apply[ Plus, e ] ] == 5, Print[ n ] ], {n, 1, 1000} ]
Select[Range[600],Abs[Total[Times@@@Partition[Riffle[IntegerDigits[#],{1,-1},{2,-1,2}],2]]]==5&] (* Harvey P. Dale, Dec 15 2012 *)
Do[ a = IntegerDigits[ n ]; l = Length[ a ]; e = o = {}; Do[ o = Append[ o, a[ [ 2k - 1 ] ]], {k, 1, l/2 + .5} ]; Do[ e = Append[ e, a[ [ 2k ] ] ], {k, 1, l/2} ]; If[ Abs[ Apply[ Plus, o ] - Apply[ Plus, e ] ] == 9, Print[ n ] ], {n, 1, 1500} ]
ds9Q[n_]:=Module[{idn=IntegerDigits[n],ker}, ker=Table[(-1)^i, {i,2,Length[idn]+1}]; First[ListCorrelate[ker,idn]]==9]; Select[Range[1000],ds9Q] (* Harvey P. Dale, Feb 14 2011 *)
okQ[n_]:=Plus@@(Times@@#&/@Partition[Most[Riffle[IntegerDigits[10n],{1,-1}]],2])==12; Select[Range[7000],okQ] (* Harvey P. Dale, Jan 17 2011 *)
okQ[n_] := Module[{d = IntegerDigits[n]}, Plus @@ Take[d, {1, Length[d], 2}] - Plus @@ Take[d, {2, Length[d], 2}] == 12]; Select[Range[7000], okQ]
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