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.

A259045 Numbers n such that n!! - 2^6 is prime.

Original entry on oeis.org

7, 9, 11, 17, 21, 27, 29, 39, 43, 45, 67, 145, 173, 613, 833, 1449, 1703, 1719, 2673, 19661, 36095, 37837, 37845
Offset: 1

Views

Author

Robert Price, Jun 17 2015

Keywords

Comments

a(24) > 50000.

Links

Crossrefs

Cf. A007749, A094144, A123910, A257864 (other forms of n!!-2^k)
Cf. A080778, A076185, A076186, A076188, A076189, A076190, A076193, A076194, A076195, A076196, A076197 (other forms of n!!+2^k)

Programs

  • Mathematica
    Select[Range[0, 50000], #!! - 64 > 0 && PrimeQ[#!! - 64] &]
Select[Range[4, 6000], PrimeQ[#!! - 64] &] (* Vincenzo Librandi, Jun 18 2015 *)

A288406 Primes of the form k!2+8, where k!2 is the double factorial number (A006852).

Original entry on oeis.org

11, 23, 113, 953, 2027033, 34459433, 7905853580633, 13113070457687988603440633, 112275575285571389562324404930670903477890633, 79777941814291672401518892224505807820921910393015244140633
Offset: 1

Views

Author

Robert Price, Jun 08 2017

Keywords

Links

Crossrefs

Cf. A076188.

Programs

  • Mathematica
    MultiFactorial[n_, k_] := If[n<1, 1, n*MultiFactorial[n-k, k]];
Select[Table[MultiFactorial[i, 2] + 8, {i, 0, 100}], PrimeQ[#]&]
Select[Range[100]!!+8,PrimeQ] (* Harvey P. Dale, May 05 2019 *)

A124247 Numbers n such that n!!-8 and n!!+8 are two consecutive primes.

Original entry on oeis.org

41, 91, 299, 341
Offset: 1

Views

Author

Farideh Firoozbakht, Nov 19 2006

Keywords

Comments

n is in the sequence iff n!!-8 and n!!+8 are primes and the four numbers n!!-2,n!!+2, n!!-4 & n!!+4 are composites. It's interesting that related to the term 341 we can say 341!!-(3+4+1) and 341!!+(3+4+1) are two consecutive primes with length 341+prime(3+4+1). Conjecture: 341 is the largest term of this sequence.

Examples

			341 is in the sequence because 341!!-8 and 341!!+8 are primes and the four numbers 341!!-2, 341!!+2, 341!!-4 & 341!!+4 are composites.

Crossrefs

Cf. A076188.

Programs

  • Mathematica
    Select[Range[5,500],PrimeQ[ #!!-8]&&PrimeQ[ #!!+8]&&!PrimeQ[ #!!-4] &&!PrimeQ[ #!!+4]&&!PrimeQ[ #!!-2]&&!PrimeQ[ #!!+2]&]
n8pQ[n_]:=Module[{x=n!!},PrimeQ[x-8]&&NextPrime[x-8]==x+8]; Select[Range[ 350],n8pQ] (* Harvey P. Dale, Jun 25 2013 *)
Previous Showing 11-13 of 13 results.

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

Content is available under The OEIS End-User License Agreement.