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 A135643 Straight-line numbers > 99. 17
 111, 123, 135, 147, 159, 210, 222, 234, 246, 258, 321, 333, 345, 357, 369, 420, 432, 444, 456, 468, 531, 543, 555, 567, 579, 630, 642, 654, 666, 678, 741, 753, 765, 777, 789, 840, 852, 864, 876, 888, 951, 963, 975, 987, 999, 1111, 1234 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers with more than two digits whose digits are in arithmetic progression. The structure of digits represent a straight line. In the graphic representation the points are connected by imaginary line segments. For a(1) to a(45) this sequence is equal to A034840. If the member of this sequence is greater than 9876543210 then the member is a repdigit number A010785. Note that the sequence of straight-line numbers starts: 10, 11, 12, ..., 98, 99, 111, 123, ... The integers with 2 digits are always straight-line numbers, but here the numbers < 100 are omitted. [Omar E. Pol, Nov 14 2009] LINKS Jens Kruse Andersen, Table of n, a(n) for n = 1..168 EXAMPLE The number 3579 is a straight-line number: . . . 9 . . . . . . 7 . . . . . . 5 . . . . . . 3 . . . . . . . . . . . . . . . MATHEMATICA Select[Range[100, 1300], Length[Union[Differences[IntegerDigits[#]]]]==1&] (* Harvey P. Dale, May 09 2012 *) PROG (Haskell) a135643 n = a135643_list !! (n-1) a135643_list = filter f [100..] where    f x = all (== 0) ws where          ws = zipWith (-) (tail vs) vs          vs = zipWith (-) (tail us) us          us = map (read . return) \$ show x -- Reinhard Zumkeller, Sep 21 2014 (PARI) is(n) = my (d=digits(n), cvx=0, ccv=0, str=0); for (i=1, #d-2, my (x=d[i]+d[i+2]-2*d[i+1]); if (x>0, cvx++, x<0, ccv++, str++)); return (cvx==0 && ccv==0 && str>0) \\ Rémy Sigrist, Aug 09 2017 CROSSREFS Cf. A010785, A034840. Cf. A135600, A135601, A135602, A135603, A135641, A135642, A163278, A167847. [Omar E. Pol, Nov 14 2009] Cf. A247616 (subsequence). Sequence in context: A280636 A039990 A034840 * A070798 A235039 A279423 Adjacent sequences:  A135640 A135641 A135642 * A135644 A135645 A135646 KEYWORD nonn,base AUTHOR Omar E. Pol, Nov 30 2007, Dec 09 2008, Nov 14 2009 STATUS approved

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Last modified October 19 14:36 EDT 2019. Contains 328222 sequences. (Running on oeis4.)