121056

Appears in sequences

• Truncated tetrahedral numbers: a(n) = (1/6)*(n+1)*(23*n^2 + 19*n + 6).at n=31A005906
• Numbers k such that phi(k) and sigma(k) are both perfect squares.at n=31A067781
• a(n) = n*(n+1)*(n+2)*(n+3)*(n+4)*(2 + 4*n + n^2)/840.at n=11A101097
• Numbers k such that phi(k)*sigma(k) is a fourth power.at n=4A114078
• G.f. satisfies A(x) = 1 + x*A(2x)^3.at n=5A171200
• Guttmann's coefficients c_n rho_n for square lattice.at n=7A259854