404358569165
domain: N
Appears in sequences
- Indices of triangular numbers which are also pentagonal.at n=11A046175
- a(n) = 5*a(n-1) - 5*a(n-2) + a(n-3) with a(1) = 1 and a(k) = 0 if k <= 0.at n=21A061278
- a(1) = least k such that 1/2+1/3+1/4+1/5 < H(k) - H(5); a(2) = least k such that H(a(1)) - H(5) < H(k) -H(a(1)), and for n > 2, a(n) = least k such that H(a(n-1)) - H(a(n-2)) > H(k) - H(a(n-1)), where H = harmonic number.at n=18A228025
- a(n) = Sum_{k=0..floor(n/2)} 2^(n-2*k) * binomial(2*n-2*k+1,2*k+1).at n=20A387694