31909

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 23.at n=8A031611
• Start of the first run of exactly n consecutive odd composite numbers.at n=23A075067
• a(n) = smallest composite (odd) number greater than a(n-1) such that a(n)+2n is the first prime after a(n).at n=23A189118
• a(n) = Sum_{k=1..n} k*lcm(k,k')/gcd(k,k'), where k' is arithmetic derivative of k.at n=27A190122
• G.f.: Product_{k>=1} (1 + 3*x^(k^2)) / (1-x^k).at n=27A280225
• Sum of the odd parts in the partitions of n into 5 parts.at n=43A309545