18625

Appears in sequences

• Number of singular 2 X 2 matrices over Z(n) (i.e., with determinant = 0).at n=24A020478
• A simple grammar.at n=10A052890
• a(n) = (prime(n)^2 + 1)/2.at n=42A066885
• a(n) is the least number k that A074389(k) = n.at n=24A074390
• Downward vertical of triangular spiral in A051682.at n=32A081272
• Number of Pythagorean quadruples mod n; i.e., number of solutions to w^2 + x^2 + y^2 = z^2 mod n.at n=24A096018
• Least k such that prime(n)^2 divides binomial(2k,k).at n=43A110494
• sigma(n) + n is a square.at n=37A114069
• Indices m such that A128646(m)-1 is prime, where A128646 = denominator of partial sums of 1/(p(i)-1).at n=49A137689
• Expansion of 1/(x^k*(1-x-2*x^(k+1))) for k=8.at n=36A143451
• a(n) = 5^(floor(n/2))+5^(floor(n/2)-1)-5^(floor((n-1)/3)).at n=10A170834
• Composite numbers k such that k = (product of divisors of k) mod (sum of divisors of k).at n=42A187712
• Number of intersections of diagonals in the interior and exterior of a regular n-gon.at n=21A211383
• Number of pairs of 2 X 2 matrices over Z/nZ that commute.at n=4A227479
• Number of partitions of n for which (number of occurrences of the least part) = (number of occurrences of greatest part).at n=45A236543
• Number of non-congruent solutions of x^2 + y^2 + z^2 + t^2 == 0 mod n.at n=24A240547
• Beastly reciprocals, or numbers k such that digitsum(1/k) = 666.at n=34A244661
• a(n) = 32*n^2 - 56*n + 25.at n=25A272129
• Number of non-congruent solutions of x^2+y^2 == z^2+w^2 (mod n).at n=24A316148
• L.g.f.: -log( Sum_{n=-oo..+oo} (-2)^n * (2*x)^(n^2) ) = Sum_{n>=1} a(n) * x^n/n.at n=6A337950