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A163278 Concave-convex numbers. 5
1010, 1011, 1020, 1021, 1022, 1023, 1030, 1031, 1032, 1033, 1034, 1035, 1040, 1041, 1042, 1043, 1044, 1045, 1046, 1047, 1050, 1051, 1052, 1053, 1054, 1055, 1056, 1057, 1058, 1059, 1060, 1061, 1062, 1063, 1064, 1065, 1066, 1067, 1068, 1069, 1070, 1071 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..10000

EXAMPLE

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

. . . . . .

. . . . . 8

. . . . 7 .

. 6 . . . .

. . . . . .

. . . . . .

. . 3 . . .

. . . 2 . .

1 . . . . .

. . . . . .

PROG

(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

CROSSREFS

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

Sequence in context: A133584 A139059 A123156 * A082461 A071998 A043640

Adjacent sequences:  A163275 A163276 A163277 * A163279 A163280 A163281

KEYWORD

base,easy,nonn

AUTHOR

Omar E. Pol, Oct 16 2009

STATUS

approved

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Last modified June 18 06:02 EDT 2021. Contains 345098 sequences. (Running on oeis4.)