31680

Appears in sequences

• Order of the group SL(2,Z_n).at n=32A000056
• Index of (the image of) the modular group Gamma(n) in PSL_2(Z).at n=43A001766
• Number of walks on square lattice.at n=4A005569
• a(n) = floor(n*(n-1)*(n-2)*(n-3)/31).at n=33A011941
• Triangle of numbers arising in enumeration of walks on square lattice.at n=31A052175
• Triangle of numbers arising in enumeration of walks on square lattice.at n=57A052176
• Jacobi form of weight 12 and index 1 for Niemeier lattice of type A_5^4 D_4 or D_4^6.at n=7A055762
• Triangle read by rows: T(n,k) is the number of labeled commutative monoids of order n with k idempotents.at n=19A058159
• Iteration of unitary-sigma function: a(1) = 2, a(n) = usigma(a(n-1)).at n=23A059460
• Scaled sums of squares.at n=4A060080
• Eighth column (k=7) of sextinomial array A063260.at n=10A063262
• Order of commutator subgroup of GL(2,Z_n) (invertible 2 X 2 matrices mod n: A000252).at n=32A065430
• Numbers k such that Omega(k) = Omega(k-1) + Omega(k-2) + Omega(k-3) + Omega(k-4) where Omega(k) denotes the number of prime factors of k, counting multiplicity.at n=29A078095
• A unitary phi reciprocal amicable number: consider two different numbers r, s which satisfy the following equation for some integer k: uphi(r) = uphi(s) = (1/k) * r * s / (r-s); or equivalently, 1/uphi(r) = 1/uphi(s) = k * (1/s - 1/r); sequence gives s numbers.at n=14A080767
• Compute S, the number of different quadratic residues modulo B for every base B. If the density S/B is smaller for B than for every B' less than B, then B is added to the sequence.at n=35A085635
• Number of conjugacy classes in the group GL(3,Z_n).at n=32A086768
• a(n) = p(n)/p(n-1), where p(n) = ( floor(n*log(n)) / Product_{j=2..pi(floor(n*log(n)))} prime(j) )!.at n=11A088301
• a(n) = sigma_3(n) - sigma_1(n).at n=29A092348
• a(n)=[(n+1)(n+2)(n+3)...(2n)]/(1+2+3+...+n).at n=5A110371
• Numbers k such that abs(RSA-1536 - 10^k) is prime, where RSA-1536 is the 463 decimal digit RSA challenge number A391940(48).at n=6A113931