130625

Appears in sequences

• a(n) = (1/3)*(n^2 + 2*n + 3)*(n+1)^2.at n=24A014820
• Numbers k such that S(k)=d(k), where S(k) is the Kempner function (A002034) and d(k) is the number of divisors of k (A000005).at n=36A073307
• Octagonal numbers equal to S*(3S - 2) with 3S - 2 = k^2 and S semiprime.at n=9A124106
• Octagonal numbers of the form C*(3C - 2) with 3C - 2 = k^2 and C a composite number.at n=11A125511
• Crystal ball sequence for the lattice C_4.at n=12A142993
• Numbers n such that psi(n) = 2*phi(n).at n=40A292390