This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A163278 #5 Aug 09 2017 20:15:21 %S A163278 1010,1011,1020,1021,1022,1023,1030,1031,1032,1033,1034,1035,1040, %T A163278 1041,1042,1043,1044,1045,1046,1047,1050,1051,1052,1053,1054,1055, %U A163278 1056,1057,1058,1059,1060,1061,1062,1063,1064,1065,1066,1067,1068,1069,1070,1071 %N A163278 Concave-convex numbers. %C A163278 Numbers with more than three digits that are not straight-line numbers (A135643), concave numbers (A135642) or convex numbers (A135641). %H A163278 Rémy Sigrist, <a href="/A163278/b163278.txt">Table of n, a(n) for n = 1..10000</a> %e A163278 The number of this sequence (A163278) is a concave-convex number: %e A163278 . . . . . . %e A163278 . . . . . 8 %e A163278 . . . . 7 . %e A163278 . 6 . . . . %e A163278 . . . . . . %e A163278 . . . . . . %e A163278 . . 3 . . . %e A163278 . . . 2 . . %e A163278 1 . . . . . %e A163278 . . . . . . %o A163278 (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 A163278 Cf. A135600, A135601, A135602, A135603, A135641, A135642, A135643. %K A163278 base,easy,nonn %O A163278 1,1 %A A163278 _Omar E. Pol_, Oct 16 2009