A163278 Concave-convex numbers.

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

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