21840

Appears in sequences

• a(n) = T(2n,n-2), T given by A027157.at n=5A027160
• a(n) = n*(n + 1)*(n + 2)*(n + 3)/2.at n=13A033486
• Theta series of extremal 3-modular even lattice in dimension 26.at n=3A034623
• Triangle read by rows. A generalization of unsigned Lah numbers, called L[4,1].at n=42A048854
• A triangle of numbers related to triangle A049325.at n=32A049410
• There are exactly n integer-sided triangles of area a(n).at n=31A051586
• At stage 1, start with a unit square. At each successive stage add 4*(n-1) new squares around outside with edge-to-edge contacts. Sequence gives number of squares (regardless of size) at n-th stage.at n=31A056640
• Number of cyclic subgroups of order 4 of general affine group AGL(n,2).at n=3A063407
• Numbers k such that phi(k)/lambda(k) increases to a record value, where phi(k) is the Euler totient function (A000010) and lambda(k) is the Carmichael lambda function (A002322).at n=19A066605
• Numbers n such that phi(sigma(n)) = 5*phi(n).at n=7A067708
• Numbers n such that sigma(n)^2 > 9*sigma_2(n) where sigma_2(n) is the sum of squares over the divisors of n.at n=9A068378
• Numbers k such that k-1, k+1 and k^2+1 are prime numbers.at n=39A070155
• Theta series of 9-dimensional odd unimodular lattice E_8 + Z.at n=8A071967
• Composite numbers requiring increasingly larger bases to become prime by base reversal.at n=22A075243
• Products of members of pairs in A075333.at n=36A075337
• Sum of divisors of (prime(n)+1)*(prime(n+1)+1)/4.at n=38A079089
• a(n) = (5*n+1)*(5*n+3)*(5*n+5).at n=5A079610
• Largest integer m such that m divides (sigma_(2n+1)(2k-1)-sigma(2k-1)) for all k>=1.at n=5A081863
• Triangle read by rows: T(n,m) = 4^m * (2*n+1)! / ( (2*n - 2*m + 1)! * (2*m)! ), row n has n+1 terms.at n=30A085840
• Numbers that can be expressed as the difference of the squares of primes in exactly ten distinct ways.at n=0A092006