%I #11 Feb 06 2015 12:25:37
%S 2,6,10,13,17,21,25,28,32,36,40,43,47,51,54,58,62,66,69,73,77,81,84,
%T 88,92,96,99,103,107,110,114,118,122,125,129,133,137,140,144,148,152,
%U 155,159,163,166,170,174,178,181,185,189,193,196,200,204,207,211,215,219
%N Second of three "least, sum, least" self-generating sequences.
%H Clark Kimberling, <a href="/A180123/b180123.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = least positive integer not yet used;
%F b(n) = n + a(n);
%F c(n) = least positive integer not yet used.
%e The three sequences, labeled a,b,c, are
%e a=(1,4,7,9,...), b=(2,6,10,13,...), c=(3,5,8,11...).
%t mex[list_, offset_] := NestWhile[# + 1 &, offset, MemberQ[list, #] &];
%t z = 100; a[1] = 1; b[1] = 1 + a[1];
%t c[1] = mex[soFar = {a[1], b[1]}, 1];
%t Do[soFar = Flatten[Join[{soFar, c[n - 1]}]];
%t a[n] = mex[soFar, c[n - 1]]; b[n] = n + a[n];
%t soFar = Flatten[Join[{soFar, a[n], b[n]}]];
%t c[n] = mex[soFar, c[n - 1]], {n, 2, z}]
%t Map[a, Range[z]](*A180122*)
%t Map[b, Range[z]](*A180123*)
%t Map[c, Range[z]](*A180124*)
%t (* _Peter J. C. Moses_, Aug 22 2014 *)
%t A180122 = Map[Floor[(1 + Sqrt[3]) #] - 1 &, Range[200]]
%t A180123 = A180122 + Range[200]
%t A180124 = Complement[Range[Last[A180122]], Flatten[{A180122, A180123}]]
%t (* _Peter J. C. Moses_, Aug 23 2014 *)
%Y Cf. A180122.
%K nonn
%O 1,1
%A _Clark Kimberling_, Aug 11 2010