210404

Appears in sequences

• Numbers k such that Fibonacci(prime(k)) is prime.at n=47A119984
• Numbers n such that sigma(n) - n = sigma(n') - n', where n' is the arithmetic derivative of n.at n=10A239726
• a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(5*k,k) / (4*k + 1).at n=7A346681