18734

Appears in sequences

• a(1) = 1; a(2) = 2; a(n) == a(k) (mod n-k) for all 1 < k < n.at n=13A002987
• McKay-Thompson series of class 30F for Monster.at n=37A058617
• Numbers n such that 5*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=25A103018
• O.g.f.: A(x) = Sum_{n>=0} x^n*Product_{k=0..n} (1 + 2^k*x).at n=8A124384
• Numbers n such that sigma(n) and sigma(sigma(n)) are both perfect squares.at n=21A134263
• Minimal value of A007947(m*(3^n-m)) with m coprime to 3.at n=12A147801
• G.f.: A(x) = exp( Sum_{n>=1} 2^(n^2)*(x*A(x))^n/n ), a power series in x with integer coefficients.at n=4A156214
• McKay-Thompson series of class 30F for the Monster group with a(0) = 1.at n=37A205977
• a(n) = n*(n + 5)*(n + 10)*(n + 15)/24.at n=19A264446
• Expansion of (chi(x) / chi(-x^6))^2 in powers of x where chi() is a Ramanujan theta function.at n=49A328790
• Products of four distinct primes between sphenic numbers (products of 3 distinct primes).at n=5A351382
• a(n) = Sum_{k=3..n} binomial(k,3) * floor(n/k).at n=25A366971
• Squarefree numbers k such that k^2 is abundant, and d^2 is nonabundant for any proper divisor d of k.at n=35A381741