641671

Appears in sequences

• Numbers k such that k and k^2 use only the digits 1, 2, 4, 6 and 7.at n=52A136993
• Let v = list of denominators of Farey series of order n (see A006843); let b(n) = Sum 1/(k*k'*(k+k')), where (k,k') are pairs of successive terms of v; a(n) = numerator of b(n).at n=11A278047