21921

Appears in sequences

• Expansion of a modular function for Gamma_0(15).at n=18A002510
• Concatenations C1 and C2 and C3 are all prime (see the comment lines).at n=9A034817
• Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 31 for n > 0.at n=7A101006
• a(n) = least k such that the remainder when 28^k is divided by k is n.at n=30A128368
• Numbers n which are both happy (A007770) and bihappy (A257795) numbers.at n=30A257950
• Number of nX6 0..1 arrays with every element equal to 0, 1, 3, 5, 6 or 8 king-move adjacent elements, with upper left element zero.at n=9A299449
• a(n) is the sum of the digits of the squares of all n-digit numbers.at n=2A333034