1801800

Appears in sequences

• Numbers k such that k = phi(sigma(phi(sigma(k)))).at n=28A067883
• Members of A097212, excluding highly composite numbers (A002182).at n=9A097213
• Smallest number having exactly n divisors d such that also d+2 is a divisor.at n=32A099476
• a(n) = Product_{k=1..n} A005117(k), the product of the first n squarefree positive integers.at n=8A111059
• Where records occur in A018892.at n=33A126098
• Numbers that are products of distinct primorial numbers (see A002110).at n=33A129912
• Area ar/6 (divided by 6) of primitive Pythagorean triangles such that perimeters are Averages of twin prime pairs, q=p+1, a=q^2-p^2, c=q^2+p^2, b=2*p*q, ar=a*b/2; s=a+b+c, s-+1 are primes.at n=17A155177
• Product of squarefree numbers less than n+1.at n=13A179215
• a(0) = 1; for n > 0, a(n) = smallest positive integer whose prime signature contains, for k = 1 to n, exactly one positive number appearing exactly k times.at n=3A182856
• Members m of A025487 such that, if k appears in m's prime signature, k-1 appears at least as often as k (for any integer k > 1).at n=25A182863
• a(n) = n$ / A055773(n), where n$ denotes the swinging factorial (A056040).at n=39A182923
• a(n) is the last defined element in the sequence n, f(n), f(f(n)), ..., where f(t) = lcm(t,(b+c)/2) with b < c smallest consecutive divisors of t with c - b > 1 and f(t) is undefined if such b, c do not exist or b + c is odd.at n=24A206034
• a(n) = the smallest number k such that Sum_{d|k} 1/tau(d) >= n.at n=22A237350
• Integers m such that there is exactly one k < m with sigma(k)/k > sigma(m)/m, sigma(m) being the sum of the divisors of m.at n=21A247022
• a(n) = the smallest number k such that floor(Sum_{d|k} 1/tau(d)) = n.at n=22A265393
• Numbers n such that Sum_{d|n} 1/tau(d) > Sum_{d|m} 1/tau(d) for all m < n.at n=38A265719
• Positions of records in A266344.at n=16A266345
• Numbers k for which sigma(k) - 4k exceeds sigma(j) - 4j for all j < k.at n=25A279091
• If 2n = 2^e1 + 2^e2 + ... + 2^ek [e1 .. ek distinct], then a(n) = A002110(e1) * A002110(e2) * ... * A002110(ek).at n=37A283477
• Smallest term of A304636 that requires exactly n iterations to reach a fixed point under the x -> A181819(x) map.at n=4A304647