21747

Appears in sequences

• a(n) = a(n-1) + a(n-2) + 1, with a(0) = 0 and a(1) = 12.at n=17A022317
• a(n) = [ a(n-1)/a(1) + a(n-1)/a(2) + ... + a(n-1)/a(n-1) ] for n >= 3, with initial terms 2,1.at n=11A022873
• Numbers n such that 2*n*k(n) is rational but not an integer, where k(n) is sum of successive remainders when computing the Euclidean algorithm for (1, 1/sqrt(n)) as defined in A086378 (MuPAD program is given there); numbers belonging to A086378 but not to A088900.at n=15A087414
• G.f.: A(x) = exp( Sum_{n>=1} (2^n + 1)^n * x^n/n ), a power series in x with integer coefficients.at n=4A155201
• Number of idempotent 3X3 -n..n matrices of rank 2.at n=11A223452