91999

Appears in sequences

• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 59 ones.at n=9A031827
• Numbers having four 9's in base 10.at n=10A043528
• Near-repdigit semiprimes with 9 as repeated digit.at n=32A105990
• a(n) = Sum_{k=0..floor(n/2)} binomial(n+4*k,n-2*k).at n=11A373904
• Expansion of (1 + x - x^3)/((1 + x - x^3)^2 - 4*x).at n=15A376785
• Expansion of 1 / ((1-x)^2 - x^6).at n=30A392541