20530

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 31.at n=3A031619
• Numbers that are divisible by 10 and are differences between two cubes in at least one way.at n=27A038854
• Numbers that contain as proper substrings every maximal prime power dividing them.at n=9A059401
• Number of (n+3) X 5 binary arrays with every 4 X 4 subblock commuting with each horizontal and vertical neighbor 4 X 4 subblock.at n=16A188098
• Least k such that k*30^n-1 , k*30^n+1, and 2*k*30^n-1 are prime; that is, twin primes and a Sophie Germain prime.at n=37A212956
• a(n) = Sum_{i=0..n} digsum_5(i)^4, where digsum_5(i) = A053824(i).at n=36A231671