123120

Appears in sequences

• Number of invertible 2 X 2 matrices mod n.at n=18A000252
• Number of 2 X 2 matrices with entries mod n and nonzero determinant.at n=18A005353
• Base 4 digital convolution sequence.at n=20A033641
• a(1) = 1; for n>1, a(n) = smallest integer > a(n-1) such that a(n)*a(i)+1 is prime for all 1 <= i <= n-1.at n=7A034881
• a(n) = n*(n-1)*(n-2)^2.at n=18A047927
• Orders of the finite groups GL_2(K) when K is a finite field with q = A246655(n) elements.at n=11A059238
• Numbers expressible in more than one way as 6^x-y^2.at n=23A134989
• Integers with exactly 100 divisors.at n=6A163816
• a(1) = 1, for n > 1: a(n) = phi(sum of the previous terms) where phi is Euler's totient function.at n=25A165931
• Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and positive even determinant.at n=11A211157
• Number of the Lipschitz quaternions in a reduced system modulo n.at n=18A227499
• Order of GL_2(p), the general linear group over F_p, where p runs through the primes.at n=7A244509
• Number of (n+2) X (4+2) 0..3 arrays with every 3 X 3 subblock row and diagonal sum equal to 0 3 5 6 or 7 and every 3 X 3 column and antidiagonal sum not equal to 0 3 5 6 or 7.at n=21A252380
• Consider numbers n = concat(w,x,y,z) such that w*x*y*z | n. Leading zeros in x, y and z allowed. Sequence lists numbers that admit at least two such concatenations.at n=23A257172
• Wiener index of graphs of f.c.c. unit cells in a line = Sum of distances in face-centered cubic grid unit cells connected in a row.at n=15A273322
• Coefficients in q-expansion of (E_4 + E_2^2)/2, where E_2 and E_4 are the Eisenstein series shown in A006352 and A004009, respectively.at n=8A282017
• Order of the finite groups GL(m,q) [or GL_m(q)] in increasing order as q runs through the prime powers.at n=14A335384
• Values of Euler's totient phi for A050498.at n=7A339883