20018

Appears in sequences

• Numbers n such that 8*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=4A103085
• Number of (n+3) X 7 0..2 matrices with each 4 X 4 subblock idempotent.at n=10A224724
• Numbers n such that usigma(usigma(n))/usigma(n) > usigma(usigma(m))/usigma(m) for all m < n, where usigma(n) is the sum of unitary divisors of n (A034448).at n=6A289126
• a(n) is the smallest number k such that psi(k) = A001615(k) is the product of n distinct primes.at n=5A291144
• a(n) is the smallest k such that usigma(k) = A002110(n), or 0 if no such k exists.at n=6A291356
• a(0) = a(1) = 1; a(n) = [x^n] Product_{k=1..n-1} (1 + x^a(k))/(1 - x^a(k)).at n=49A296387
• Numbers with property that both the digit sum and the sum of the prime factors (counted with multiplicity) have only digits 0 and 1 in base 10.at n=15A297614
• Expansion of Product_{k>=1} (1 + x^k)^A000593(k).at n=22A301800
• Expansion of 1/(1 - x*Sum_{k>=0} x^(k^3)).at n=21A302019