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 A110623 Shadow of N (natural numbers), also of Champernowne's shadow. 2
 1, 13, 16, 20, 25, 31, 38, 46, 55, 65, 76, 197, 511, 526, 687, 758, 839, 1759, 1761, 1883, 1906, 1930, 2182, 2244, 2316, 2398, 3328, 3641, 3874, 3908, 3943, 3979, 4016, 4399, 5339, 5380, 5422, 5465, 5509, 5554, 6018, 6092, 6176, 7126, 7177, 7229, 7282, 7336 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS First differences are N's shadow. Never twice the same integer in sequence or first differences (except the starting "1"). LINKS Petros Hadjicostas, Table of n, a(n) for n = 1..130 EXAMPLE The first line hereunder is the sequence, the second line gives the first differences: 1..13.16.20.25.31.38.46.55..65..76...197..228..269..311 ... .12..3..4..5..6..7..8..9..10..11..121...31...41...51... <-- N's shadow (which, when concatenated, gives A033307) MATHEMATICA a[1] = 1; a[n_] := a[n] = Block[{c = Flatten[ IntegerDigits /@ Range[150]], 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, 48}] (* Robert G. Wilson v, Oct 10 2005 *) CROSSREFS Cf. A000027, A007376, A033307. Sequence in context: A295327 A179202 A159975 * A163674 A280062 A132947 Adjacent sequences:  A110620 A110621 A110622 * A110624 A110625 A110626 KEYWORD base,easy,nonn AUTHOR Alexandre Wajnberg and Eric Angelini, Sep 14 2005 EXTENSIONS Corrected and extended by Robert G. Wilson v, Oct 10 2005 STATUS approved

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Last modified October 15 15:14 EDT 2019. Contains 328030 sequences. (Running on oeis4.)