A124375
Numbers k such that A003422(k+1)/2 is prime.
Original entry on oeis.org
2, 3, 4, 7, 8, 9, 10, 29, 75, 162, 270, 272, 353, 720, 1795, 3732, 4768, 9315, 12220, 41531
Offset: 1
-
f=0;Do[f=f+n!;If[PrimeQ[f/2],Print[{n,f/2}]],{n,0,353}]
Flatten[Position[Accumulate[(Range[0,12220]!)]/2,?PrimeQ]]-1 (* _Harvey P. Dale, Jul 02 2019 *)
A124374
Primes of the form !(k + 1)/2 = Sum_{i=0..k} i!/2.
Original entry on oeis.org
2, 5, 17, 2957, 23117, 204557, 2018957, 4578979328975537786697650470157, 12572230784049013026617689884981971446439568309146114097251787122217783800812199225999909965168264460210470157
Offset: 1
-
f=0;Do[f=f+n!;If[PrimeQ[f/2],Print[{n,f/2}]],{n,0,353}]
A288451
Numbers n such that !n + 7 is prime.
Original entry on oeis.org
0, 3, 4, 5, 7, 10, 12, 20, 37, 52, 73, 149, 304, 540, 2135, 7112, 7436, 9357
Offset: 1
4 is a term, because 0! + 1! + 2! + 3! + 7 = 17 is prime.
-
Do[ If[ PrimeQ[ Sum[ k!, {k, 0, n - 1} ] + 7 ], Print[ n ] ], {n, 1, 600} ]
Join[{0},Flatten[Position[Accumulate[Range[0,600]!]+7,?PrimeQ]]] (* The program generates the first 14 terms. To generate more increase the Range constant, but the program may take a long time to run. *) (* _Harvey P. Dale, May 21 2021 *)
-
s=0; for(n=0,600,if(ispseudoprime(s + 7),print1(n,", ")); s+=n!)
Showing 1-3 of 3 results.
Comments