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

Author

Omar E. Pol, Oct 16 2009

Keywords

• base
• easy
• nonn

Comments

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

Examples

			The number of this sequence (A163278) is a concave-convex number:
. . . . . .
. . . . . 8
. . . . 7 .
. 6 . . . .
. . . . . .
. . . . . .
. . 3 . . .
. . . 2 . .
1 . . . . .
. . . . . .
		

Links

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

Crossrefs

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

Programs

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