21387

Appears in sequences

• a(1) = 3; a(n) = smallest number such that the forward as well as the reverse n-th partial concatenation is a prime for n>1. (Reverse concatenation is taken term-wise and not digit-wise).at n=39A083993
• Number of spiro bicyclic skeletons with n carbon atoms.at n=8A107278
• a(n) = a(n-1) + a(floor(n/2)) + a(ceiling(n/2)).at n=35A131205
• Least j such that 6*p(j)*M(n)-1 is prime with p(j)=j-th prime and M(n) = Mersenne prime.at n=28A157333
• a(n) = 74*n^2 + 1.at n=17A158742
• Stack polyominoes with square core.at n=45A188674
• Number of integer partitions of n whose parts do not have choosable sets of integer partitions.at n=38A387134