21877

Appears in sequences

• a(n) is the smallest composite number c such that A002110(n) + c is prime.at n=29A038771
• a(1) = 1; set of digits of a(n)^2 is a subset of the set of digits of a(n+1)^2.at n=27A066825
• Denominators of the convergents of the continued fraction expansion [1;1/2,1/3,1/4,...,1/n,...].at n=9A092053
• a(n) = number of distinct values of Product_{i=1..r} x_i!*i!^x_i, where (x_1, ..., x_r) is an r-tuple of nonnegative integers with Sum_{i=1..r} i*x_i = n.at n=49A102465
• a(n) = a(n-2) + 2^(n-1) + 5 for n>3, a(0..3) = (0,1,2,7).at n=15A147672
• Number of (n+2) X (3+2) 0..3 arrays with every 3 X 3 subblock row and diagonal sum equal to 0 3 5 6 or 7 and every 3 X 3 column and antidiagonal sum not equal to 0 3 5 6 or 7.at n=16A252379
• Semiprimes whose prime factors are of equal binary length and which differ from each other in exactly two bit positions.at n=45A261074
• Numbers that are the sum of eight fourth powers in nine or more ways.at n=32A345584
• Numbers that are the sum of eight fourth powers in exactly nine ways.at n=17A345841
• E.g.f. satisfies A(x) = exp( (exp(x) - 1) * A(x)^(x^2) ).at n=7A362800