26208

Appears in sequences

• Number of invertible 2 X 2 matrices mod n.at n=12A000252
• Index of (the image of) the modular group Gamma(n) in PSL_2(Z).at n=38A001766
• Theta series of extremal 3-modular even 24-dimensional lattice with minimal norm 6 and det = 3^12.at n=3A004046
• Number of 2 X 2 matrices with entries mod n and nonzero determinant.at n=12A005353
• Expansion of (1-x^7)/(1-x)^7.at n=13A008489
• a(n) is the concatenation of n and 8n.at n=25A009470
• Theta series of D*_28 lattice.at n=3A022081
• Theta series of A*_8 lattice.at n=49A023920
• Numbers k such that the set of prime divisors of k is equal to the set of prime divisors of sigma(k).at n=15A027598
• Numbers k such that 247*2^k+1 is prime.at n=25A032500
• Cycle of 3 steps possible for 'concatenate a(n) and nextprime(a(n)) is a prime'.at n=7A034593
• Duplicate of A004046.at n=3A034622
• Number of points of l_1 norm n in the "diamond" lattice D^+_4.at n=27A035878
• a(n) = n*(n-1)*(n-2)^2.at n=12A047927
• a(n) = Sum_{d|n, n/d=1 mod 4} d^3 - Sum_{d|n, n/d=3 mod 4} d^3.at n=29A050471
• Numbers k such that sigma(k) = 7k/2.at n=2A055153
• Triangle of coefficients of Gandhi polynomials.at n=25A058942
• Orders of the finite groups GL_2(K) when K is a finite field with q = A246655(n) elements.at n=8A059238
• Nonpalindromic numbers k such that k is not divisible by 10 and k*R(k) is a square, where R(k) is the reversal of k (A004086).at n=27A062917
• a(n) = the maximum number of lattice points touched by an origin-centered 4d-sphere with radius <= n.at n=34A071345