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.

Showing 1-5 of 5 results.

A134932 a(n)=A134928(n)/2.

Original entry on oeis.org

2, 3, 4, 5, 6, 7, 8, 9, 10, 14, 15, 16, 20, 21, 22, 29, 30, 31, 35, 36, 37, 50, 51, 52, 53, 54, 55, 68, 69, 70, 74, 75, 76, 89, 90, 91, 95, 96, 97, 98, 99, 100, 113, 114, 115, 119, 120, 121, 134, 135, 136, 140, 141, 142, 155, 156, 157
Offset: 1

Views

Author

Omar E. Pol, Nov 22 2007

Keywords

Comments

Triplet composites, divided by 2.

Examples

			a(6)=7 because A134928(6)=14 then we can write 14/2=7.

Crossrefs

Cf. A134928.

A153809 Complement of A134928.

Original entry on oeis.org

1, 2, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 22, 23, 24, 25, 26, 27, 29, 31, 33, 34, 35, 36, 37, 38, 39, 41, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59, 61, 63, 64, 65, 66, 67, 68, 69, 71, 73, 75, 76, 77, 78, 79, 80, 81
Offset: 1

Views

Author

Omar E. Pol, Jan 27 2009

Keywords

Crossrefs

Cf. A134928, A134932.

A134930 Nearest-neighbors of twin primes.

Original entry on oeis.org

2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 28, 30, 32, 40, 42, 44, 58, 60, 62, 70, 72, 74, 100, 102, 104, 106, 108, 110, 136, 138, 140, 148, 150, 152, 178, 180, 182, 190, 192, 194, 196, 198, 200, 226, 228, 230, 238, 240, 242, 268, 270, 272, 280, 282, 284
Offset: 1

Views

Author

Omar E. Pol, Nov 16 2007

Keywords

Comments

This sequence consists of the number 2 followed by the triple composites: A134928.

Examples

			2, 4 and 6 are nearest-neighbors of twin primes because 3 and 5 are twin primes.

Links

Programs

  • Mathematica
    f[{a_,b_}]:={a-1,a+1,b+1}; Union[Flatten[f/@Select[Partition[Prime[ Range[ 100]],2,1], Last[#]-First[#]==2&]]] (* Harvey P. Dale, Aug 16 2011 *)

Formula

a(1)=2. For n>2, a(n)=A134928(n-1)

A210940 The prime numbers and their nonprime nearest-neighbors.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 22, 23, 24, 28, 29, 30, 31, 32, 36, 37, 38, 40, 41, 42, 43, 44, 46, 47, 48, 52, 53, 54, 58, 59, 60, 61, 62, 66, 67, 68, 70, 71, 72, 73, 74, 78, 79, 80, 82, 83, 84, 88, 89, 90, 96, 97, 98, 100
Offset: 1

Views

Author

Omar E. Pol, Apr 17 2012

Keywords

Comments

The prime numbers and their nearest-neighbors without repetitions.

Crossrefs

Union of A210939 and A000040. Complement of A079364.
Cf. A018252, A045718, A134928, A134930.

Programs

  • Mathematica
    {#-1,#,#+1}&/@Prime[Range[30]]//Flatten//Union (* Harvey P. Dale, Jul 06 2019 *)

Extensions

Corrected (74 added) by Harvey P. Dale, Jul 06 2019

A210939 Nonprime nearest-neighbors of the primes.

Original entry on oeis.org

1, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 28, 30, 32, 36, 38, 40, 42, 44, 46, 48, 52, 54, 58, 60, 62, 66, 68, 70, 72, 74, 78, 80, 82, 84, 88, 90, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 126, 128, 130, 132, 136, 138, 140, 148, 150, 152, 156
Offset: 1

Views

Author

Omar E. Pol, Apr 17 2012

Keywords

Comments

Essentially the same as A147819. R. J. Mathar, Jun 25 2012

Crossrefs

Nonprimes in A045718.
Cf. A000040, A018252, A134928, A134930, A210940.

Programs

  • Mathematica
    Select[Range[156], ! PrimeQ[#] && (PrimeQ[# - 1] || PrimeQ[# + 1]) &] (* T. D. Noe, Apr 18 2012 *)
Join[{1},Flatten[#+{-1,1}&/@Prime[Range[3,40]]]//Union] (* Harvey P. Dale, Oct 22 2022 *)
Showing 1-5 of 5 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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