521728

Appears in sequences

• Numbers k such that sigma(k) == 4 (mod k).at n=10A045769
• Numbers k such that sigma(k) == 0 (mod k+2).at n=8A067702
• Numbers k whose abundance is 4: sigma(k) - 2*k = 4.at n=7A088832
• Admirable numbers such that the subtracted divisor is prime.at n=12A109766
• Admirable numbers whose abundance is < 10.at n=27A109788
• Abundant numbers n for which the abundance d = sigma(n) - 2*n is a proper divisor, that is, 0 < d < n and d | n.at n=39A181595
• (N\{4})-perfect numbers, i.e., numbers m for which sigma(m)-4 = 2m, if 4|m, otherwise sigma(m) = 2m.at n=5A181597
• Near-perfect numbers (A181595) of the form 2^(t-1)*(2^t-2^k-1), where 2^t-2^k-1 is prime, k>=1, t>k.at n=21A181701
• Numbers m=2^(t-1)*(2^t-5), where 2^t-5 is prime.at n=4A181704
• 1-sequence of reduction of the upper Wythoff sequence by x^2 -> x+1.at n=19A192303
• Number of ways to place 2 non-attacking wazirs on an n X n toroidal board.at n=31A201236
• Admirable numbers such that the subtracted divisor is a Fibonacci number.at n=27A282754
• Practical numbers (A005153) that are abundant and have a record low value of abundancy index.at n=17A362052
• Primitive abundant numbers k (A071395) whose abundancy index sigma(k)/k has a record low value.at n=18A362053