1284121

Appears in sequences

• Semiprimes pq with pq - 1 divisible by p + q.at n=26A164643
• Numerators b(n) of Pythagorean approximations b(n)/a(n) to 3/2.at n=5A195551
• Denominators a(n) of Pythagorean approximations b(n)/a(n) to 2/3.at n=10A195559
• Bi-unitary k-hyperperfect numbers: numbers m such that m = 1 + k * (bsigma(m) - m - 1) where bsigma(m) is the sum of bi-unitary divisors of m (A188999) and k >= 1 is an integer.at n=34A309568