A193407 -id:A193407 - cp's OEIS frontend

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 111, 121, 131, 141, 151, 161, 171, 181, 191, 222, 232, 242, 252, 262, 272, 282, 292, 333, 343, 353, 363, 373, 383, 393, 444, 454, 464, 474, 484, 494, 555, 565, 575, 585, 595, 666, 676, 686, 696, 777, 787, 797, 888, 898, 999, 1111, 1221, 1231, 1241, 1251, 1261, 1271, 1281, 1291, 1321, 1331

Offset: 1

Jaroslav Krizek, Jul 25 2011

Another version of mountain numbers (A134941) and A193407.
For n > 20 the structure of digits represents a hill. The first digit is equal to the last digit (1 - 9). The first digits are in nondecreasing order. The last digits are in nonincreasing order. The numbers may have more than one largest digit. Sequence is infinite.
Superset of mountain numbers (A134941), A193407, and Giza numbers (A134810).
Superset of A110784. - R. J. Mathar, Aug 07 2011

			Illustration using a term of this sequence, 4566664:
  .  .  6  6  6  6  .
  .  5  .  .  .  .  .
  4  .  .  .  .  .  4

Cf. A110784, A134810, A134941, A193407.

nonz[v_] := Select[v,#!=0 &]; hillQ[n_] := Module[{d=IntegerDigits[n]}, If[d[[1]] != d[[-1]], Return[False]]; MemberQ[{{},{0},{-2}}, nonz@ Differences@ Sign@ nonz@ Differences@d]]; Select[Range[1000], hillQ] (* Amiram Eldar, Dec 19 2018 *)

cp's OEIS Frontend

A193408 Hill numbers.

Views

Author

Keywords

Comments

Examples

Crossrefs

Programs

Mathematica