40640

Appears in sequences

• Numbers k such that (k, sigma(k)) lies on a circle with integral radius centered at the origin, i.e., k^2 + sigma(k)^2 is a square.at n=28A066764
• Numbers k such that gcd(sigma(k),k) = k/5.at n=15A067237
• Arithmetic mean of two consecutive prime interprimes of second order: interprimes of third order.at n=11A126556
• Numbers d*p where d is a perfect number and p<d a prime not dividing d.at n=29A165772
• E.g.f. A(x) satisfies A( x/(exp(3*x)*cosh(3*x)) ) = exp(4*x)*cosh(4*x).at n=4A218309
• Numbers k for which sigma(k)/k - 2/5 is an integer.at n=4A218407
• Larger member of primitive friendly pairs ordered by smallest maximal element.at n=30A233039
• Numbers n with the property that it is possible to write the base 2 expansion of n as concat(a_2,b_2), with a_2>0 and b_2>0 such that, converting a_2 and b_2 to base 10 as a and b, we have sigma(a)*sigma(b) = n.at n=20A244079
• Number of tilings of a 12 X n rectangle using 3*n copies of the disconnected shape [o_oo_o].at n=29A320437
• Numbers k for which sigma(k)/k = 12/5.at n=4A347222
• Numbers k such that the continued fraction of the abundancy index of k contains a single distinct element.at n=19A349686
• Smallest integer that is the sum of a prime and the square of a prime in exactly n ways.at n=32A381334