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 11-13 of 13 results.

A262578 Concatenation of the numbers from 1 to n but omitting 8.

Original entry on oeis.org

1, 12, 123, 1234, 12345, 123456, 1234567, 12345679, 1234567910, 123456791011, 12345679101112, 1234567910111213, 123456791011121314, 12345679101112131415, 1234567910111213141516, 123456791011121314151617, 12345679101112131415161718, 1234567910111213141516171819, 123456791011121314151617181920
Offset: 1

Views

Author

N. J. A. Sloane, Sep 25 2015

Keywords

Comments

The first (probable) prime in this sequence is a(1872) = 1234567910111213...1873 (ending at 1873), a 6384-digit probable prime, too large to display here. It was found by David Broadhurst on Sep 27 2015.
No other primes through a(10000). - Robert Price, Nov 04 2018
a(1872) is prime. - Jason Yuen, Nov 17 2024

Crossrefs

See A262300 for more about this problem.

Programs

  • Mathematica
    Module[{nn=30, c}, c=Drop[Range[nn], {8}]; Table[FromDigits[Flatten[IntegerDigits/@Take[c, n]]], {n, nn-1}]] (* Vincenzo Librandi, Nov 05 2018 *)

A262579 Concatenation of the numbers from 1 to n but omitting 9.

Original entry on oeis.org

1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 1234567810, 123456781011, 12345678101112, 1234567810111213, 123456781011121314, 12345678101112131415, 1234567810111213141516, 123456781011121314151617, 12345678101112131415161718, 1234567810111213141516171819, 123456781011121314151617181920
Offset: 1

Views

Author

N. J. A. Sloane, Sep 25 2015

Keywords

Comments

There are only two primes among the first 98 terms, namely
1234567810111213141516171819 and 1234567810111213141516171819202122232425262728293031323334353637.
Does this sequence contain any other primes?
No other primes through a(10000). - Robert Price, Nov 04 2018

Crossrefs

See A262300 for more about this problem.

Programs

  • Mathematica
    DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {9}]]]], {n, 20}]] (* Robert Price, Nov 05 2018 *)
    Module[{nn=20,c},c=Drop[Range[nn],{9}];Table[FromDigits[Flatten[ IntegerDigits/@ Take[c,n]]],{n,nn-1}]] (* Harvey P. Dale, Nov 30 2019 *)

A262580 Concatenation of the numbers from 1 to n but omitting 10.

Original entry on oeis.org

1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678911, 1234567891112, 123456789111213, 12345678911121314, 1234567891112131415, 123456789111213141516, 12345678911121314151617, 1234567891112131415161718, 123456789111213141516171819, 12345678911121314151617181920
Offset: 1

Views

Author

N. J. A. Sloane, Sep 25 2015

Keywords

Comments

The smallest prime in this sequence is the 61457-digit (probable) prime a(14512) = 123456789111213...14513 found by David Broadhurst on Sep 28 2015.

Crossrefs

See A262300 for more about this problem.

Programs

  • Mathematica
    DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {10}]]]], {n, 20}]] (* Robert Price, Nov 05 2018 *)
Previous Showing 11-13 of 13 results.