222531

Appears in sequences

• a(n+3) = a(n+2) + 3a(n+1) - 2a(n); a(0) = 1, a(1) = -1, a(2)= 3.at n=20A104005
• Semiprimes sp = p^2 + q^2 + r^2 where p, q and r are consecutive primes.at n=11A242209
• Expansion of (1 + x + 21*x^2 + x^3 + x^4)/(1 - x)^5.at n=21A257602