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.

A383241 a(n) = p(n)*p(n+1)*(p(n+1) - p(n)) - 1, where p(n) = prime(n).

Original entry on oeis.org

5, 29, 69, 307, 285, 883, 645, 1747, 4001, 1797, 6881, 6067, 3525, 8083, 14945, 18761, 7197, 24521, 19027, 10365, 34601, 26227, 44321, 69063, 39187, 20805, 44083, 23325, 49267, 200913, 66547, 107681, 38085, 207109, 44997, 142241, 153545, 108883, 173345
Offset: 1

Views

Author

Clark Kimberling, May 07 2025

Keywords

Examples

			a(n) = A383242(n) - 2.

Crossrefs

Cf. A000042, A383242, A383243, A383244.

Programs

  • Mathematica
    z = 60; p[n_] := Prime[n];
f[n_] := p[n]*p[n + 1]*(p[n + 1] - p[n])
Table[f[n] - 1, {n, 1, z}]  (* A383241 *)
Table[f[n] + 1, {n, 1, z}]  (* A383242 *)

A383242 a(n) = p(n)*p(n+1)*(p(n+1) - p(n)) + 1, where p(n) = prime(n).

Original entry on oeis.org

7, 31, 71, 309, 287, 885, 647, 1749, 4003, 1799, 6883, 6069, 3527, 8085, 14947, 18763, 7199, 24523, 19029, 10367, 34603, 26229, 44323, 69065, 39189, 20807, 44085, 23327, 49269, 200915, 66549, 107683, 38087, 207111, 44999, 142243, 153547, 108885, 173347
Offset: 1

Views

Author

Clark Kimberling, May 07 2025

Keywords

Crossrefs

Cf. A000042, A383241, A383243, A383244.

Programs

  • Mathematica
    z = 60; p[n_] := Prime[n];
f[n_] := p[n]*p[n + 1]*(p[n + 1] - p[n])
Table[f[n] - 1, {n, 1, z}]  (* A383241 *)
Table[f[n] + 1, {n, 1, z}]  (* A383242 *)

Formula

a(n) = A383241(n) + 2.

A383244 Primes of the form p(k)*p(k+1)*(p(k+1) - p(k)) + 1 sorted by increasing k.

Original entry on oeis.org

7, 31, 71, 647, 4003, 6883, 3527, 14947, 34603, 20807, 23327, 173347, 73727, 503869, 103967, 145799, 450403, 194687, 669283, 848203, 1193443, 1775563, 649799, 1976803, 2088547, 2131243, 4687069, 2534947, 2581963, 5338237, 3250123, 3411043, 1555847, 5346763
Offset: 1

Views

Author

Clark Kimberling, May 07 2025

Keywords

Comments

Conjecture: there are infinitely many such primes.

Crossrefs

Cf. A000042, A383241, A383243.
Primes in A383242.

Programs

  • Maple
    =q:= 2; R:= NULL: count:= 0:
while count < 100 do
  p:= q;
  q:= nextprime(q);
  v:= p*q*(q-p)+1;
  if isprime(v) then R:= R,v; count:= count+1 fi;
od:
R; # Robert Israel, May 11 2025
  • Mathematica
    z = 200; p[n_] := Prime[n];
f[n_] := p[n]*p[n + 1]*(p[n + 1] - p[n])
t1 = Table[f[n] - 1, {n, 1, z}];    (* A383241 *)
t2 = Table[f[n] + 1, {n, 1, z}];    (* A383242 *)
Select[t1, PrimeQ[#] &]  (* A383243 *)
Select[t2, PrimeQ[#] &]  (* A383244 *)
  • PARI
    select(isprime, vector(200, k, prime(k)*prime(k+1)*(prime(k+1) - prime(k)) + 1)) \\ Michel Marcus, May 12 2025
Showing 1-3 of 3 results.

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

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