%I A110621
%S A110621 1,4,18,33,42,44,50,55,90,98,195,288,311,395,457,521,859,891,898,1848,
%T A110621 1876,2717,3688,3757,3796,4733,5243,5301,5321,6295,6389,6434,6526,6556,
%U A110621 6634,6650,6690,7318,7938,8027,9013,9293,9327,9409,9462,9883,10053
%N A110621 Shadow of Pi.
%C A110621 First differences are Pi's shadow. Never twice the same integer in sequence 
               or first differences.
%e A110621 The first line hereunder is the sequence, the second line are the first 
               differences:
%e A110621 1.4..18..33.42.44.50.55..90.98..195..288..311...
%e A110621 .3.14..15..9..2..6..5..35..8..97...93...23 <-- Pi shadow
%e A110621 (Pi=3.141592653589793238462643383279502884197169399...)
%t A110621 a[1] = 1; a[n_] := a[n] = Block[{c = RealDigits[Pi, 10, 300][[1]], k 
               = 1, t = Table[a[i], {i, n - 1}]}, d = Drop[t, 1] - Drop[t, -1]; 
               b = Drop[c, Length[ Flatten[ IntegerDigits /@ d]]]; e = Union[ Join[t, 
               d]]; While[f = FromDigits[ Take[b, k]]; Position[e, f] != {} || b[[k 
               + 1]] == 0, k++ ]; f + a[n - 1]]; Table[ a[n], {n, 47}] (* Robert 
               G. Wilson v *)
%Y A110621 Cf. A000796.
%Y A110621 Sequence in context: A095823 A092116 A083969 this_sequence A124978 A031081 
               A009956
%Y A110621 Adjacent sequences: A110618 A110619 A110620 this_sequence A110622 A110623 
               A110624
%K A110621 easy,nonn,base
%O A110621 1,2
%A A110621 Eric Angelini & Alexandre Wajnberg (eric.angelini(AT)kntv.be), Sep 14 
               2005
%E A110621 More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Oct 10 2005