21182

Appears in sequences

• a(n) = 1*t(n) + 2*t(n-1) + ... + k*t(n+1-k), where k=floor((n+1)/2) and t = A008578 ({1} U primes).at n=39A023862
• a(n) = 1*prime(n) + 2*prime(n-1) + ... + k*prime(n+1-k), where k=floor((n+1)/2) and prime(n) is the n-th prime.at n=38A023870
• Consider all integer triples (i,j,k), j >= k > 0, with binomial(i+2,3)=j^3+k^3, ordered by increasing i; sequence gives k values.at n=25A054207
• a[n] =a[n-1] + 2*n*Prime[n]-n^2.at n=21A093809
• Grow a binary tree using the following rules. Initially there is a single node labeled 1. At each step we add 1 to all labels less than 3. If a node has label 3 and zero or one descendants we add a new descendant labeled 1. Sequence gives sum of all labels at step n.at n=43A123015
• Numbers n such that pi(n^2)=pi((n-k)^2)+n, where k=A000193(n).at n=40A137271
• Number of conjugacy classes in simply connected twisted Chevalley group 2E6(q) as q runs through the prime powers.at n=3A225934
• Pentagonal numbers that are also Niven numbers.at n=31A242043
• Number of length n+2 0..5 arrays with no three consecutive terms having the sum of any two elements equal to twice the third.at n=3A248458
• T(n,k)=Number of length n+2 0..k arrays with no three consecutive terms having the sum of any two elements equal to twice the third.at n=31A248461
• Number of length 4+2 0..n arrays with no three consecutive terms having the sum of any two elements equal to twice the third.at n=4A248465
• Expansion of Product_{k>=1} ((1 + x)^k + x^k)/((1 + x)^k - x^k).at n=22A307521
• Smallest k > 0 with gcd(k, rev(k)) = n, where rev(k) is digit reversal of k and with sum of digits of k = n, or 0 if no such k exists.at n=13A333666
• Number of ways to write n as an ordered sum of 7 primes (counting 1 as a prime).at n=23A341986
• Pentagonal numbers which are products of four distinct primes.at n=19A381919
• Number of finite regions in a complete bipartite graph where the vertices in the two parts are placed on opposite sides of a parabola at integer x coordinates |x| = 1, 2, ...n.at n=17A392426