login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A241425 Largest number k > 0 such that n + k! and n - k! are both prime, or 0 if no such k exists. 2
0, 0, 0, 1, 2, 1, 0, 0, 2, 0, 3, 1, 3, 0, 2, 0, 3, 1, 0, 0, 2, 0, 3, 0, 3, 0, 0, 0, 4, 1, 0, 0, 0, 0, 4, 0, 4, 0, 2, 0, 0, 1, 4, 0, 2, 0, 4, 0, 0, 0, 0, 0, 3, 0, 4, 0, 0, 0, 0, 1, 0, 0, 0, 0, 4, 0, 3, 0, 2, 0, 0, 1, 3, 0, 0, 0, 4, 0, 0, 0, 2, 0, 4, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

If k > n, n - k! is surely negative and, therefore, not prime.

a(n) < A020639(n). - Robert Israel, Aug 10 2014

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

a:= proc(n)

local k;

for k from min(numtheory:-factorset(n))-1 to 1 by -1 do

  if n > k! and isprime(n+k!) and isprime(n-k!) then return(k) fi

od:

0

end proc:

a(1):= 0:

seq(a(n), n=1..100); # Robert Israel, Aug 10 2014

PROG

(PARI)

a(n)=forstep(k=n, 1, -1, if(ispseudoprime(n+k!)&&ispseudoprime(n-k!), return(k)))

n=1; while(n<150, print1(a(n), ", "); n++)

CROSSREFS

Cf. A020639, A245716, A241423, A241424.

Sequence in context: A298931 A035219 A245716 * A106347 A124300 A154326

Adjacent sequences:  A241422 A241423 A241424 * A241426 A241427 A241428

KEYWORD

nonn

AUTHOR

Derek Orr, Aug 08 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 26 16:52 EDT 2020. Contains 334627 sequences. (Running on oeis4.)