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 1-4 of 4 results.

A078154 Primes of the form A004154(k) + 1.

Original entry on oeis.org

2, 3, 7, 13, 73, 871782913, 1307674369, 62044840173323943937, 33078854415193864122595302822125378214568325182093497117061192683541123570097156545925087233
Offset: 1

Views

Author

Cino Hilliard, Dec 23 2002

Keywords

Comments

More precisely, scan A004154, add 1 and record the answer if it is a prime. The sequence may not be monotonic.
The next term is too large to include.

Crossrefs

Programs

  • Magma
    [a: n in [1..100] | IsPrime(a) where a is Factorial(n) div 10^Valuation(Factorial(n), 5)+1]; // Vincenzo Librandi, Jun 03 2016

Extensions

More terms from Joshua Zucker, Jan 11 2006

A078190 Primes of the form A004154(n) - 1.

Original entry on oeis.org

5, 23, 11, 71, 503, 62270207, 871782911, 121645100408831, 243290200817663, 304888344611713860501503, 137637530912263450463159795815809023
Offset: 1

Views

Author

Cino Hilliard, Dec 23 2002

Keywords

Comments

More precisely, scan A004154, subtract 1 and record the answer if it is a prime. The sequence is not monotonic.

Crossrefs

Programs

  • Maple
    A004154 := proc(n) option remember ; local m ; if n <= 1 then RETURN(1) ; else m := A004154(n-1)*n ; while m mod 10 = 0 do m := m /10 ; end ; RETURN(m) ; fi ; end: n := 1 ; while true do f := A004154(n) : if isprime(f-1) then printf("%d, ",f-1) ; fi ; n := n+1 : od : # R. J. Mathar, Feb 27 2007
  • PARI
    v=[];for(n=1,500,if(ispseudoprime(t=n!/10^valuation(n!,5)-1),v=concat(v,t))); v \\ Charles R Greathouse IV, Feb 14 2011

Extensions

More terms from R. J. Mathar, Feb 27 2007

A078203 Numbers k such that A004154(k) + 1 is prime.

Original entry on oeis.org

1, 2, 3, 5, 6, 14, 15, 24, 74, 191, 222, 276, 2200, 3041, 3701, 4324, 6201
Offset: 1

Views

Author

Cino Hilliard, Dec 23 2002

Keywords

Crossrefs

Programs

  • Mathematica
    f[n_] := n!/10^Sum[ Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ f[n] + 1], Print[n]], {n, 1, 850}]

Extensions

Extended by Joshua Zucker, Robert G. Wilson v and Jason Earls, Dec 24 2002
a(13) from Don Reble, Jan 12 2006
a(14)-a(17) from Michael S. Branicky, Jul 23 2023

A079154 Numbers k such that reverse(A004154(k)) - 1 is prime.

Original entry on oeis.org

3, 4, 12, 30, 33, 1406
Offset: 1

Views

Author

Jason Earls and Robert G. Wilson v, Dec 27 2002

Keywords

Comments

The values corresponding to a(1)-a(6) have been certified prime with Primo. a(7) > 15000. - Giovanni Resta, Feb 20 2013
a(7) > 40000. - Michael S. Branicky, Jan 05 2025

Crossrefs

Programs

  • Mathematica
    f[n_] := n!/10^Sum[Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[ f[n]]]] - 1], Print[n]], {n, 1, 800}]

Extensions

a(6) from Giovanni Resta, Feb 20 2013
Showing 1-4 of 4 results.