OFFSET
1,2
COMMENTS
Numbers n such that ((n+{0,1})-th prime-1)^2+1 are both primes.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1)=1 because ((1+0)-th prime-1)^2+1=2=prime and ((1+1)-th prime-1)^2+1=5=prime; a(2)=2 because ((2+0)-th prime-1)^2+1=5=prime and ((2+1)-th prime-1)^2+1=17=prime
MAPLE
P:= select(isprime, [2, seq(i, i=3..10^6, 2)]):
J:= select(i -> isprime((P[i]-1)^2+1), {$1..nops(P)}):
sort(convert(J intersect map(`-`, J, 1), list)); # Robert Israel, Sep 29 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Feb 18 2010
EXTENSIONS
126 removed. Terms beyond 247 added by R. J. Mathar, Mar 01 2010
STATUS
approved