30730

Appears in sequences

• Numbers k such that sigma(k) = sigma(k+8).at n=29A015876
• Number of binary operations on an n-set that are commutative and associative; labeled commutative semigroups.at n=5A023815
• a(n) = a(n-1) + floor((a(n-2) + a(n-3))/2), with a(n)=1 for n < 3.at n=26A214041
• Numbers whose squares remain squares when prepended with 5 and appended with 25 in base 10.at n=1A249971
• Integers k such that 2^k-1 has 0 as its second-most significant digit in base k.at n=8A385924
• Triangle read by rows: T(n,k) is the number of labeled semigroups with n elements whose center contains k elements.at n=20A391157