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A178333 Characteristic function of mountain numbers. 5
0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(A134941(n)) = 1; a(A134951(n)) = 1;

a(n) = 0 for n > 12345678987654321;

a(A011540(n))=0; a(A052383(n))=0; a(A171901(n))=0;

A178334(n) = SUM(a(k): 0<=k<=n).

LINKS

R. Zumkeller, Table of n, a(n) for n = 0..20000

Index entries for characteristic functions

FORMULA

a(n) = if n mod 10 = 1 then if n = 1 then 1 else g(n div 10, 1) else 0

with g(x, y) = if x mod 10 > y then g(x div 10, x mod 10) else if x mod 10 = y then 0 else h(x div 10, x mod 10)

and h(x, y) = if y = 1 then 0^x else if x mod 10 < y then h(x div 10, x mod 10) else 0.

MATHEMATICA

a[n_] := Boole[ MatchQ[ IntegerDigits[n], {1, a___, b_, c___, 1} /; OrderedQ[{1, a, b}, Less] && OrderedQ[ {b, c, 1}, Greater]]]; a[1]=1; Table[a[n], {n, 0, 200}] (* Jean-Fran├žois Alcover, Jun 13 2012 *)

PROG

(Haskell)

a178333 n = fromEnum $

   n `mod` 10 == 1 && a000030 n == 1 && a196368 n == 1 && and down where

      down = dropWhile (== False) $ zipWith (<) (tail $ show n) (show n)

a178333_list = map a178333 [0..]

-- Reinhard Zumkeller, Oct 28 2001

CROSSREFS

Cf. A000030, A196368.

Sequence in context: A173950 A157928 A159075 * A063524 A326168 A033683

Adjacent sequences:  A178330 A178331 A178332 * A178334 A178335 A178336

KEYWORD

nonn,base

AUTHOR

Reinhard Zumkeller, May 25 2010

STATUS

approved

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Last modified January 19 09:35 EST 2020. Contains 331048 sequences. (Running on oeis4.)