253007

Appears in sequences

• Numbers k such that p-k=p#-k#, where p=nextprime(k), k#=nextprime(square root of k), p#=nextprime(square root of p).at n=10A037210
• a(n) = number of tuples (a,b,c,d) of natural numbers a,b,c,d <= n with gcd(a,b)=gcd(b,c)=gcd(c,d)=gcd(d,a)=1.at n=31A256391