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A166342
Numbers n such that (n+2)*n!*Sum((-1)^k/k!),k=0..n+2 is prime.
0
2, 3, 4, 8, 13, 42, 64, 166, 573, 1711
OFFSET
1,1
COMMENTS
No further terms up to n=20000. The sequence a[n]=(n+2)*n!*Sum((-1)^k/k!),k=0..n+2 is A000255.
FORMULA
n is an index of the sequence a[n]=(n+2)*n!*Sum((-1)^k/k!),k=0..n+2 such that a[n] is prime.
EXAMPLE
For n=3, a[3]=11 which is prime.
PROG
(PARI) z_even=1; z_odd=1;
for(n=1, 20000,
if(n%2==1,
z_odd=(n+2)*(n-1)*z_odd+1; if((ispseudoprime(z_odd)), print(n="n)),
z_even=(n+2)*(n-1)*z_even-1; if((ispseudoprime(z_odd)), print(n="n))); );
CROSSREFS
Cf. A000255 (corresponding sequence).
Sequence in context: A361722 A092075 A091415 * A361502 A091816 A266400
KEYWORD
nonn
AUTHOR
Mike Oakes, Oct 12 2009
STATUS
approved