131215

Appears in sequences

• Describe the n-th triangular number A000217(n).at n=25A045986
• a(n) equals the (n*(n+1)/2)-th partial sum of the self-convolution 4th power of A010054, which has the g.f.: Sum_{k>=0} x^(k*(k+1)/2).at n=25A109415
• Row sums of the array A274193, defined by g(n,k) = 1 for n >= 0; g(n,k) = 0 if k > n; g(n,k) = g(n-1,k-1) + g(n-1,3k) for n > 0, k > 1.at n=42A274194
• a(n) is the binary XOR of all n-bit prime numbers.at n=17A298817