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A163278 Concave-convex numbers. 5

%I

%S 1010,1011,1020,1021,1022,1023,1030,1031,1032,1033,1034,1035,1040,

%T 1041,1042,1043,1044,1045,1046,1047,1050,1051,1052,1053,1054,1055,

%U 1056,1057,1058,1059,1060,1061,1062,1063,1064,1065,1066,1067,1068,1069,1070,1071

%N Concave-convex numbers.

%C Numbers with more than three digits that are not straight-line numbers (A135643), concave numbers (A135642) or convex numbers (A135641).

%H Rémy Sigrist, <a href="/A163278/b163278.txt">Table of n, a(n) for n = 1..10000</a>

%e The number of this sequence (A163278) is a concave-convex number:

%e . . . . . .

%e . . . . . 8

%e . . . . 7 .

%e . 6 . . . .

%e . . . . . .

%e . . . . . .

%e . . 3 . . .

%e . . . 2 . .

%e 1 . . . . .

%e . . . . . .

%o (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) \\ _Rémy Sigrist_, Aug 09 2017

%Y Cf. A135600, A135601, A135602, A135603, A135641, A135642, A135643.

%K base,easy,nonn

%O 1,1

%A _Omar E. Pol_, Oct 16 2009

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Last modified July 30 04:44 EDT 2021. Contains 346348 sequences. (Running on oeis4.)