A242040 Numbers n such that n + k! and n - k! are both prime for some k.
4, 5, 6, 9, 11, 12, 13, 15, 17, 18, 21, 23, 25, 29, 30, 35, 37, 39, 42, 43, 45, 47, 53, 55, 60, 65, 67, 69, 72, 73, 77, 81, 83, 85, 95, 99, 102, 103, 105, 107, 108, 111, 113, 125, 127, 129, 131, 133, 137, 138, 143, 145, 149, 150, 151, 155, 157, 161, 163, 165, 173, 175, 180, 185, 187
Offset: 1
Keywords
Examples
5 + 2! = 7 and 5 - 2! = 3 are both prime. Thus 5 is a member of this sequence.
Links
- Jens Kruse Andersen, Table of n, a(n) for n = 1..10000
Programs
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PARI
a(n)=for(k=1,n,if(ispseudoprime(n+k!)&&ispseudoprime(n-k!),return(k))) n=1;while(n<500,if(a(n),print1(n,", "));n++)
Comments