51850

Appears in sequences

• Number of singular 2 X 2 matrices over Z(n) (i.e., with determinant = 0).at n=33A020478
• Write the numbers from 1 to n^2 in a spiraling square; a(n) is the total of the sums of the two diagonals.at n=34A059924
• Numbers k such that the sum of the Carmichael lambda functions of the divisors is a proper divisor of k.at n=28A131492
• a(n) = 10^n mod 3^n.at n=10A139734
• Number of n X 4 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=16A207449
• For every positive integer m, let u(m) = (d(1),d(2),...,d(k)) be the unitary divisors of m. The sequence (a(n)) consists of integers of the form d(k)/d(1) + d(k-1)/d(2) + ... + d(k)/d(1).at n=15A229999
• n^n mod 3^n.at n=10A233398
• Number of length-n binary words such that every conjugate (cyclic shift) is rich.at n=20A306316
• Primitive abundant numbers version 2 (abundant numbers all of whose proper divisors are deficient numbers) and increasing any prime factor in the prime factorization gives a non-abundant number when factored back.at n=39A335557
• Number of cells in a regular 7-gon after n generations of mitosis.at n=38A349808
• a(1)=1; a(2)=4; for n>2, a(n) = a(n-1) + A000217(n)*a(n-2).at n=7A351046
• Primitive nondeficient numbers satisfying a stronger condition that compares abundancy with related numbers as detailed in the comments.at n=22A352739
• a(n) = Sum_{1 <= x_1, x_2 <= n} sigma( n/gcd(x_1, x_2, n) ).at n=33A373129
• a(n) is the least number k such that there is a set of n proper divisors of k whose sum is k, and no set of fewer than n proper divisors of k whose sum is k.at n=15A389712