OFFSET
1,2
COMMENTS
The shadow of the decimal expansion of a constant (here: A001113) is defined as a sequence of integers such that (i) the concatenation of the first differences reproduces the decimal expansion, (ii) no integer appears more than once in the sequence or its first differences, (iii) at each step the smallest possible number of digits of the constant is swallowed to define the first differences, not leaving a leading zero behind.
EXAMPLE
The first line hereunder is the sequence, the second line gives the first differences:
1.3.10..28...309.317...601.606..696.700..752..787...1147...1434..1481...
.2.7..18..281...8...284...5...90...4...52...35...360....287....47 <-- "e" shadow
e = 2.71828182845904523536028747135266249775724709369995...
MATHEMATICA
a[1] = 1; a[n_] := a[n] = Block[{c = RealDigits[E, 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, 41}] (* Robert G. Wilson v *)
KEYWORD
base,easy,nonn
AUTHOR
Eric Angelini and Alexandre Wajnberg, Sep 14 2005
EXTENSIONS
Corrected and extended by Robert G. Wilson v, Oct 10 2005
Comment expanded by R. J. Mathar, Jun 15 2010
STATUS
approved