26977

Appears in sequences

• Hyperperfect numbers: k = m*(sigma(k) - k - 1) + 1 for some m > 1.at n=13A007592
• Numbers k such that the continued fraction for sqrt(k) has period 87.at n=19A020426
• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 36.at n=3A031624
• Hyperperfect numbers: x such that x = 1 + k*(sigma(x)-x-1) for some k > 0.at n=17A034897
• Number of n X n binary arrays symmetric under horizontal and vertical reflection with all ones connected only in a 0110-1111 pattern in any orientation.at n=13A146383
• Semiprimes pq with pq - 1 divisible by p + q.at n=9A164643
• Unitary hyperperfect numbers.at n=20A225150
• Generalized Markoff numbers: largest of 7-tuple of positive numbers a, b, c, d, e, f, g satisfying the Markoff(7) equation a^2+b^2+c^2+d^2+e^2+f^2+g^2 = 2abcdefg.at n=29A227210
• 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=15A309568
• Smallest integer m = b*c which satisfies (b + c)*n = m - 1.at n=47A364169