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 A131744 Eric Angelini's "1995" puzzle: the sequence is defined by the property that if one writes the English names for the entries, replaces each letter with its rank in the alphabet and calculates the absolute values of the differences, one recovers the sequence. 13
 1, 9, 9, 5, 5, 9, 9, 5, 5, 9, 1, 3, 13, 17, 1, 3, 13, 17, 9, 5, 5, 9, 9, 5, 5, 9, 1, 3, 13, 17, 1, 3, 13, 17, 9, 5, 5, 9, 10, 1, 9, 15, 12, 10, 13, 0, 15, 12, 1, 9, 2, 15, 0, 9, 5, 14, 17, 17, 9, 6, 15, 0, 9, 1, 1, 9, 15, 12, 10, 13, 0, 15, 12, 1, 9, 2, 15, 0, 9, 5, 14, 17, 17, 9 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS In the first few million terms, the numbers 16, 19, 20 and 22-26 do not occur. Of the numbers that do occur, the number 11 appears with the smallest frequence - see A133152. - N. J. A. Sloane, Sep 22 2007 From David Applegate, Sep 24 2007: (Start) The numbers 16, 19-20, 22-25 never occur in the sequence. The following table gives the possible numbers that can occur in the sequence and for each one, the possible numbers that can follow it. The table is complete - when any number and its successor are expanded, the resulting pairs are also in the table. It contains the expansion of 1 and thus describes all possible transitions: 0 -> 0,1,4,5,7,9,10,12,15,21 1 -> 1,3,5,9,12 2 -> 1,3,12,15 3 -> 0,1,2,3,4,5,8,9,11,12,13,14,18 4 -> 2,3,12,14 5 -> 3,5,9,10,12,14,15 6 -> 3,5,12,15,21 7 -> 7,10,17 8 -> 0,3,5,9 9 -> 0,1,2,3,4,5,6,8,9,10,12,14,15,21 10 -> 1,13,15,17 11 -> 21 12 -> 0,1,6,9,10,14,15,21 13 -> 0,3,17 14 -> 3,10,15,17 15 -> 0,3,4,9,12,15,18 17 -> 1,9,10,14,15,17,21 18 -> 3,7,9 21 -> 13,21 (End) The sequence may also be extended in the reverse direction: ... 0 21 21 13 3 0 [then what we have now] 1 9 9 5 5 ..., corresponding to ... zero twentyone twentyone thirteen three zero one nine nine five ... - N. J. A. Sloane, Sep 27 2007 The name of this sequence ("Eric Angelini's ... puzzle") was added by N. J. A. Sloane many months after Eric Angelini submitted it. Begin with 1, map the integer to its name and then map according to A073029, compute the absolute difference, spell out that difference; iterate as necessary. - Robert G. Wilson v, Jun 08 2010 LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..40000 EXAMPLE O.N.E...N.I.N.E...N.I.N.E...F.I..V..E...F.I..V..E... .1.9..9..5.5.9..9..5.5.9..1..3.13.17..1..3.13.17.... 1 -> "one" -> 15,14,5 -> (the difference is) 1,9; iterate. Therefore 1,9 -> "one,nine"; -> 15,14,5,14,9,14,5 -> 1,9,9,5,5,9; "one,nine,nine,five,five,nine"; etc. - Robert G. Wilson v, Jun 08 2010 MATHEMATICA tra = {"a" -> 1, "b" -> 2, "c" -> 3, "d" -> 4, "e" -> 5, "f" -> 6, "g" -> 7, "h" -> 8, "i" -> 9, "j" -> 10, "k" -> 11, "l" -> 12, "m" -> 13, "n" -> 14, "o" -> 15, "p" -> 16, "q" -> 17, "r" -> 18, "s" -> 19, "t" -> 20, "u" -> 21, "v" -> 22, "w" -> 23, "x" -> 24, "y" -> 25, "z" -> 26}; trn = {0 -> "zero", 1 -> "one", 2 -> "two", 3 -> "three", 4 -> "four", 5 -> "five", 6 -> "six", 7 -> "seven", 8 -> "eight", 9 -> "nine", 10 -> "ten", 11 -> "eleven", 12 -> "twelve", 13 -> "thirteen", 14 -> "fourteen", 15 -> "fifteen", 17 -> "seventeen", 18 -> "eighteen", 21 -> "twentyone"}; f[n_] := (aa = IntegerDigits@n /. trn; bb = Characters@aa /. tra // Flatten; cc = Flatten@ Abs[ Most@bb - Rest@bb]); Nest[f@# &, {1}, 4] (* Robert G. Wilson v, Jun 08 2010 *) CROSSREFS Cf. A131745, A131746, A130316, A133152, A133816, A133817. Cf. A131285 (ranks of letters), A131286, A131287. Cf. A001477 (see its b-file). - Robert G. Wilson v, Jun 08 2010 Sequence in context: A117232 A155995 A229191 * A076416 A201289 A091133 Adjacent sequences:  A131741 A131742 A131743 * A131745 A131746 A131747 KEYWORD nonn,word,nice AUTHOR Eric Angelini, Sep 20 2007 EXTENSIONS More terms from N. J. A. Sloane, Sep 20 2007 STATUS approved

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Last modified December 13 06:26 EST 2019. Contains 329968 sequences. (Running on oeis4.)