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 1-3 of 3 results.

A139460 a(n) = m such that 2*prime(n+m+1) + (product of n successive odd primes) is prime.

Original entry on oeis.org

1, 1, 1, 1, 2, 3, 3, 1, 1, 2, 1, 1, 9, 2, 7, 21, 7, 25, 4, 3, 18, 7, 4, 7, 11, 5, 1, 1, 61, 5, 20, 6, 22, 16, 11, 17, 1, 70, 6, 5, 5, 22, 9, 52, 108, 16, 1, 32, 42, 15, 5, 66, 6, 8, 3, 38, 17, 4, 23, 93, 8, 16, 6, 1, 39, 7, 9, 10, 21, 57, 40, 2, 15, 39, 16, 7, 5, 13, 138, 95, 58, 8, 47, 11, 39
Offset: 1

Views

Author

Artur Jasinski, Apr 22 2008; definition corrected May 09 2008

Keywords

Comments

Or, a(n) = m such that primorial(n+1)/2+2*prime(n+m+1) is prime.
For positions of 1's in this sequence see A139461

Crossrefs

Cf. A067026, A067027, A139439, A139440, A139441, A139442, A139443, A139444, A139445, A139446, A139447, A139448, A139449, A139450, A139451, A139452, A139453, A139454, A139455, A139456, A139457, A103514, A139460, A139461, A139462, A139463.

Programs

  • Mathematica
    k = 1; a = {}; Do[k = k*Prime[n]; m = 1; While[ ! PrimeQ[k + 2*Prime[n + m]], m++ ]; Print[m]; AppendTo[a, m], {n, 2, 200}]; a (*Artur Jasinski*)

A139462 a(n) = m such that product n successive odd primes - 2*prime(n+m+1) is prime = such m that primorial(n+1)/2 - 2*prime(n+m+1) is prime.

Original entry on oeis.org

1, 2, 1, 1, 3, 1, 2, 2, 3, 1, 6, 5, 5, 7, 1, 5, 8, 2, 10, 29, 3, 7, 10, 8, 33, 28, 11, 3, 19, 5, 12, 12, 11, 19, 52, 29, 17, 23, 29, 36, 3, 1, 7, 59, 16, 5, 4, 113, 1, 8, 16, 25, 4, 5, 52, 1, 82, 71, 14, 34, 20, 3, 1, 35, 20, 107, 14, 38, 41, 34, 14, 6, 20, 36, 36, 20, 62, 19, 8, 92, 140
Offset: 1

Views

Author

Artur Jasinski, Apr 22 2008

Keywords

Comments

For indices where 1 occurs, see A139463.

Crossrefs

Cf. A067026, A067027, A139439, A139440, A139441, A139442, A139443, A139444, A139445, A139446, A139447, A139448, A139449, A139450, A139451, A139452, A139453, A139454, A139455, A139456, A139457, A103514, A139460, A139461, A139462, A139463.

Programs

  • Mathematica
    k = 1; a = {}; Do[k = k*Prime[n]; m = 1; While[ ! PrimeQ[k - 2*Prime[n + m]], m++ ]; Print[m]; AppendTo[a, m], {n, 2, 200}]; a (*Artur Jasinski*)

A139463 Numbers n such that (product of the first n odd primes) - 2*prime(n+2) is a prime.

Original entry on oeis.org

3, 4, 6, 10, 15, 42, 49, 56, 63, 106, 170, 182, 246, 255, 507, 627, 848, 864, 961, 1302, 3209, 4994, 7665, 7671, 16405
Offset: 1

Views

Author

Artur Jasinski, Apr 22 2008

Keywords

Comments

a(26) > 25000. - Robert Price, Sep 27 2017

Examples

			3 is in the sequence because 3*5*7 - 2*11 = 83 is a prime.

Crossrefs

Cf. A067026, A067027, A139439, A139440, A139441, A139442, A139443, A139444, A139445, A139446, A139447, A139448, A139449, A139450, A139451, A139452, A139453, A139454, A139455, A139456, A139457, A103514, A139460, A139461, A139462.

Programs

  • Mathematica
    k = 1; a = {}; Do[k = k*Prime[n]; If[PrimeQ[k - 2*Prime[n + 1]], AppendTo[a, n - 1]], {n, 2, 2000}]; a
  • PARI
    isok(n) = isprime(prod(k=2, n+1, prime(k)) - 2*prime(n+2)); \\ Michel Marcus, Sep 27 2017

Extensions

Edited by Jens Kruse Andersen, May 03 2008
a(15)-a(25) from Robert Price, Sep 27 2017
Showing 1-3 of 3 results.

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

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