9840770

Appears in sequences

• a(n) = 1 + a(floor(n/2))*a(ceiling(n/2)) for n > 1, a(1) = 2.at n=19A005469
• See Comments for definition.at n=5A121264
• a(n) = 531441*n^2 - 740664*n + 258065.at n=4A157667
• Numbers n such that sigma(n-1) and sigma(n) - 1 are both primes.at n=16A270415