21505

Appears in sequences

• 4-dimensional analog of centered polygonal numbers: a(n) = n(n+1)*(n^2+n+4)/12.at n=22A006007
• Sextuple factorial numbers: Product_{k=0..n-1} (6*k + 5).at n=4A008543
• Triangle read by rows, the inverse Bell transform of n!*binomial(5,n) (without column 0).at n=10A013988
• Odd octagonal numbers: (2n+1)*(6n+1).at n=42A014641
• Quotients k*(k+1)*(k+2) / (k+(k+1)+(k+2)) that are lucky numbers.at n=18A032792
• a(n) = (n-1)*(2*n-1)*(3*n-1)*(4*n-1).at n=6A033593
• a(n) is square mod a(i), i < n; a(n) nonsquare; a(1) = 2.at n=18A034901
• a(1)=10; if n = Product p_i^e_i, n > 1, then a(n) = Product p_{i+1}^e_i * Product p_{i+3}^e_i.at n=38A045973
• T(n,n-5), where T is the array in A055830.at n=21A055832
• Product of first n primes of form 6k-1.at n=3A057130
• Number of solutions of x^5=1 in general affine group AGL(n,2).at n=3A063388
• Consider the power series (x + 1)^(1/3) = 1 + x/3-x^2/9 + 5x^3/81 + ...; sequence gives numerators of coefficients.at n=9A067622
• Odd numbers k such that the number of 1's in binary representation of k equals omega(k), the number of distinct primes in the factorization of k.at n=26A071595
• a(n) = Sum_{d|n} (2^(n-d)).at n=14A074854
• Pair the odd numbers such that the k-th pair is (r, r+2k) where r is the smallest odd number not included earlier: (1, 3), (5, 9), (7, 13), (11, 19), (15, 25), (17, 29), (21, 35), (23, 39), (27, 45), ... This is the sequence of the product of the members of pairs.at n=35A075320
• An interleaved sequence of pyramidal and polygonal numbers.at n=43A081283
• Smallest d such that real quadratic field with discriminant d has class number n.at n=27A081364
• Sextuple factorials, 6-factorials, n!!!!!!, n!6.at n=23A085158
• Numbers with exactly one arithmetic progression of four successive divisors (not necessarily consecutive).at n=19A094530
• Values of k such that the total number of 1's in the binary expansions of the first k integers is a multiple of k.at n=23A095376