21903

Appears in sequences

• a(n) = 16n^2 + 32n + 15.at n=36A141759
• a(1)=3; for n > 1, a(n) = 1 + a(n-1) + gcd( a(n-1)*(a(n-1)+2), A073829(a(n-1)) ).at n=33A167053
• a(n) = (8*n+3)*(8*n+5).at n=18A177065
• Numbers k such that tau(k+1) - tau(k) = 3, where tau(k) = the number of divisors of k (A000005).at n=9A230653
• Numbers of the form 16n^2 + 32n + 15 for which the central region of its symmetric representation of sigma consists of two subparts of sizes 4n+7 and 4n+1, n>=0.at n=30A335574