515970

Appears in sequences

• a(n) = Product_{k=1..n} sigma(k)/d(k), where sigma(k) = Sum_{j|k} j and d(k) = Sum_{j|k} 1. Set a(n) = 0 if the corresponding product is not an integer (e.g., for n=2 and n=10).at n=11A109361
• The number of tilings of an equilateral triangle of side length n with k lozenges and n^2 - 2*k unit triangles. Triangle T(n, k) with n >= 1 and 0 <= k <= n*(n + 1)/2, read by rows.at n=30A273464
• Nonsquare positive integers k such that k = a*b = c*m + b and b^2 = a*m + c where m > 1, 0 < a, b, c < m.at n=12A347168