81209

Appears in sequences

• a(n) = (10n+1)*(10n+9).at n=28A001535
• Expansion of 1/(1 + x * Sum_{k>=1} prime(k)*x^k).at n=28A307899
• a(n) = determinant([a(n-1), a(n-2); a(n-4), a(n-3)]) for n >= 5, a(n) = n otherwise.at n=10A337188