20520
domain: N
Appears in sequences
- Index of (the image of) the modular group Gamma(n) in PSL_2(Z).at n=37A001766
- 4-dimensional figurate numbers: a(n) = n*binomial(n+2, 3).at n=17A002417
- Expansion of (1-x)^(-3) * (1-x^2)^(-2).at n=34A002624
- Alkane (or paraffin) numbers l(7,n).at n=29A005994
- [ n(n-1)(n-2)(n-3)/7 ].at n=21A011917
- a(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026681.at n=5A026989
- a(n) = binomial(n+2, 2) + binomial(n+4, 5).at n=17A027658
- Even 10-gonal (or decagonal) numbers.at n=36A028994
- Base 4 digital convolution sequence.at n=17A033641
- Number of partitions of n into parts not of the form 17k, 17k+6 or 17k-6. Also number of partitions with at most 5 parts of size 1 and differences between parts at distance 7 are greater than 1.at n=39A035967
- Triangle read by rows, giving T(n,k) = number of k-member minimal ordered covers of a labeled n-set (1 <= k <= n).at n=19A049055
- When expressed in base 2 and then interpreted in base 3, is a multiple of the original number.at n=23A062845
- Order of commutator subgroup of GL(2,Z_n) (invertible 2 X 2 matrices mod n: A000252).at n=37A065430
- Sum of divisors of 2^n+1.at n=13A069061
- First differences of A069475, successive differences of (n+1)^6-n^6.at n=26A069476
- a(n) = n*(n-1)*(2*n^2 + 1)/6.at n=16A071245
- Numbers k not in A065036 but such that tau(k) = omega(k)^3.at n=18A074853
- Expansion of exp(3x)/sqrt(1-x^2).at n=7A081921
- Bisection of A002417.at n=8A100431
- a(n) = binomial(n+2,2)*binomial(n+5,2).at n=14A105938