21630

Appears in sequences

• Numbers k such that the least term in the periodic part of the continued fraction for sqrt(k) is 14.at n=21A031692
• Numbers k such that 213*2^k+1 is prime.at n=16A032483
• Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= n/2.at n=18A047167
• Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= (n-1)/2.at n=18A047178
• Consider the Diophantine equation x^3 + y^3 = z^3 + 1 (1 < x < y < z) or 'Fermat near misses'. Sequence gives values of z in monotonic increasing order.at n=19A050791
• Cube of lower triangular matrix of A056857 (successive equalities in set partitions of n).at n=40A078938
• Numbers k such that 7*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=14A103057
• A071605(n)/(n-1)!.at n=6A135474
• Subsequence of 'Fermat near misses' which is generated by a simple formula based on the cubic binomial expansion along with formulas for the corresponding terms in the expression, x^3 + y^3 = z^3 + 1.at n=6A141326
• 6 times octagonal numbers: a(n) = 6*n*(3*n-2).at n=35A153796
• Half the number of length n integer sequences with sum zero and sum of squares 4418.at n=3A157579
• a(n) = 441*n^2 + 21.at n=7A158603
• Diagonal sums of number triangle [k<=n]*C(n,2n-2k)3^(n-k)A000108(n-k).at n=15A160568
• a(n) = 49*n^2 + n.at n=20A173141
• Least even number m which can be written as sum of 2n primes p(1) < ... < p(2n) < m/2 such that m-p(i) is also prime for i=1,...,2n.at n=29A191837
• a(n) = A220371(n)/(4*A220371(n-1)).at n=25A193365
• Number T(n,k) of equivalence classes of ways of placing k 9 X 9 tiles in an n X n square under all symmetry operations of the square; irregular triangle T(n,k), n>=9, 0<=k<=floor(n/9)^2, read by rows.at n=51A236936
• Consider a number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that phi(n) = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(j)*10^(j-1)})} (see example below).at n=6A240897
• Main diagonal of square arrays A114881 and A249741.at n=24A249743
• Number of length n 1..(2+2) arrays with no leading partial sum equal to a prime and no consecutive values equal.at n=16A255710