51985

Appears in sequences

• Number of singular 2 X 2 matrices over Z(n) (i.e., with determinant = 0).at n=36A020478
• Number of noninvertible 2 X 2 matrices over Z/nZ (determinant is a divisor of 0).at n=35A020479
• Numbers k that, when expressed in base 5 and then interpreted in base 8, give a multiple of k.at n=44A062930
• Diagonal in array of n-gonal numbers A081422.at n=36A081437
• Number of pairs with two different elements which can be obtained by selecting unique elements from two sets with n+1 and n^2 elements respectively and n common elements.at n=37A085490
• Number of Pythagorean quadruples mod n; i.e., number of solutions to w^2 + x^2 + y^2 = z^2 mod n.at n=36A096018
• Triangle read by rows, derived from a(n) = N*a(n-1) + a(n-2).at n=30A138765
• a(n) = 36*n^2 + 1.at n=38A158591
• Number of non-congruent solutions of x^2 + y^2 + z^2 + t^2 == 0 mod n.at n=36A240547
• Numbers of the form m^2 + 1 that can be expressed in more than one way as j^2 + k^2 with j > k > 1 and gcd(j,k) = 1.at n=31A300166
• Number of non-congruent solutions of x^2+y^2 == z^2+w^2 (mod n).at n=36A316148
• Numbers k such that sigma(k)^2 is divisible by k-1.at n=38A344347
• Let q be the n-th prime power (A246655), then a(n) = q^3 + q^2 - q; number of solutions to x*y = z*w in the finite field F_q.at n=18A367014
• a(n) = Sum_{1 <= x_1, x_2 <= n} sigma( n/gcd(x_1, x_2, n) ).at n=36A373129