cp's OEIS Frontend

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.

Previous Showing 11-14 of 14 results.

A182776 Mountain nonprimes.

Original entry on oeis.org

1, 121, 141, 161, 171, 1241, 1251, 1261, 1271, 1281, 1341, 1351, 1371, 1391, 1421, 1431, 1461, 1491, 1521, 1541, 1561, 1581, 1591, 1631, 1641, 1651, 1671, 1681, 1691, 1731, 1751, 1761, 1781, 1791, 1821, 1841, 1851, 1891, 1921, 1941, 1961, 1971, 1981, 12321, 12341, 12351, 12361, 12371
Offset: 1

Views

Author

Omar E. Pol, Dec 14 2010

Keywords

Comments

The total number of terms is 19226. The largest is 12345678987654321 which is also the largest Giza number A134810.

Examples

			a(2)=121 is in the sequence because 121 is a nonprime number A018252 and 121 is also a mountain number A134941.
Illustration of 134961 as a mountain nonprime:
. . . 9 . .
. . . . . .
. . . . . .
. . . . 6 .
. . . . . .
. . 4 . . .
. 3 . . . .
. . . . . .
1 . . . . 1

Crossrefs

Cf. A018252, A134810, A134941, A134951.

Formula

A018252 INTERSECT A134941.

A193407 Mountain numbers (version 2).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 121, 131, 141, 151, 161, 171, 181, 191, 232, 242, 252, 262, 272, 282, 292, 343, 353, 363, 373, 383, 393, 454, 464, 474, 484, 494, 565, 575, 585, 595, 676, 686, 696, 787, 797, 898, 1231, 1241, 1251, 1261, 1271, 1281, 1291, 1321
Offset: 1

Views

Author

Jaroslav Krizek, Jul 25 2011

Keywords

Comments

Another version of mountain numbers (A134941).
For n > 9 the structure of digits represents a mountain. The first digit is equal to the last digit (1 - 9). The first digits are in increasing order. The last digits are in decreasing order. The numbers only have one largest digit. This sequence is finite. The final term is 12345678987654321.

Examples

			Illustration using the member of this sequence - number 56789765:
  .  .  .  .  9  .  .  .
  .  .  .  8  .  .  .  .
  .  .  7  .  .  7  .  .
  .  6  .  .  .  .  6  .
  5  .  .  .  .  .  .  5

Crossrefs

Supersequence of mountain numbers (A134941) and Giza numbers (A134810). Subsequence of hill numbers (A193408).

A193408 Hill numbers.

Original entry on oeis.org

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

Views

Author

Jaroslav Krizek, Jul 25 2011

Keywords

Comments

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

Examples

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

Crossrefs

Cf. A110784, A134810, A134941, A193407.

Programs

  • Mathematica
    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 *)

A182775 Giza nonprimes.

Original entry on oeis.org

1, 4, 6, 8, 9, 121, 232, 343, 454, 565, 676, 898, 12321, 23432, 45654, 56765, 67876, 78987, 1234321, 2345432, 3456543, 4567654, 5678765, 6789876, 123454321, 234565432, 456787654, 567898765, 12345654321, 23456765432, 45678987654
Offset: 1

Views

Author

Omar E. Pol, Dec 16 2010

Keywords

Comments

I propose the name Giza nonprimes.
The total number of terms is 37. The largest is 12345678987654321 which is also the largest mountain number A134941.

Examples

			a(6)=121 is in the sequence because 121 is a nonprime number A018252 and 121 is also a Giza number A134810.
The last six terms of this finite sequence are
a(32) = 1234567654321
a(33) = 2345678765432
a(34) = 3456789876543
a(35) = 123456787654321
a(36) = 234567898765432
a(37) = 12345678987654321
Illustration of a(37) as a Giza nonprime:
. . . . . . . . 9 . . . . . . . .
. . . . . . . 8 . 8 . . . . . . .
. . . . . . 7 . . . 7 . . . . . .
. . . . . 6 . . . . . 6 . . . . .
. . . . 5 . . . . . . . 5 . . . .
. . . 4 . . . . . . . . . 4 . . .
. . 3 . . . . . . . . . . . 3 . .
. 2 . . . . . . . . . . . . . 2 .
1 . . . . . . . . . . . . . . . 1

Crossrefs

Cf. A018252, A134810, A134811, A134941, A182776.

Programs

  • Mathematica
    Select[Union[FromDigits/@Select[Flatten[Table[Table[Join[Range[i,i+n], Reverse[ Most[ Range[ i,i+n]]]],{n,0,9}],{i,9}],1],Max[#]<10&]], !PrimeQ[#]&] (* Harvey P. Dale, Aug 23 2011 *)

Formula

A018252 INTERSECT A134810.
Previous Showing 11-14 of 14 results.

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