19836

Appears in sequences

• Numbers n such that sigma(n)^2 - phi(n)^2 is a perfect square.at n=40A057654
• Number of polyhexes with n cells that tile the plane by 180-degree rotation (Conway criterion) but not by translation.at n=10A075210
• Expansion of (1-x)^(-1)/(1+x+x^2-2*x^3).at n=23A077907
• 12 times hexagonal numbers: 12*n*(2*n-1).at n=29A143698
• Row sums of triangle A144825.at n=37A144826
• 4 times 9-gonal numbers: a(n) = 2*n*(7*n-5).at n=38A152760
• Number of integer-sided pentagons having perimeter n, modulo rotations but not reflections.at n=40A293822