142560

Appears in sequences

• Numbers k such that phi(sigma(k)) = k.at n=9A001229
• Numbers k such that sigma(phi(sigma(k))) = sigma(k).at n=19A066471
• Numbers k such that k = phi(sigma(phi(sigma(k)))).at n=21A067883
• Numbers k such that k = phi(sigma(phi(sigma(phi(sigma(k)))))).at n=21A067884
• a(1) = 1, a(n) = a(n-1) if n = 1 (mod 3), otherwise n*a(n-1).at n=10A123144
• a(n) = denominator of Product_{k=1..n} (1 + {n/k}), where {x} is the fractional part of x, {x} = x - floor(x).at n=12A128779
• Numbers k such that sigma_2(k)*sigma_1(k)/sigma_0(k) is a perfect square.at n=18A152218
• Smallest size of which there are n tatami-free rooms.at n=27A165764
• a(n) = v(n+1)/v(n), where v=A203430.at n=6A203431
• Take the squares of all P_(n+2)-rough numbers less than the (n+1)-th primorial and mod each by the (n+1)-th primorial. There will be a(n) different results.at n=7A246541
• Young urn sequence (number of possible evolutions in n steps of the "Young" Pólya urn).at n=7A293653
• a(n) is the number of residues modulo (4*primorial(n)) of the squares of primes greater than or equal to prime(n+1).at n=9A323739
• Number of compositions (ordered partitions) of n into distinct prime powers (including 1).at n=42A331925
• E.g.f. satisfies A(x)^A(x) = 1/(1 - x)^(x^2).at n=9A356910
• Numbers which are the minimum of a cycle in the map x -> phi(sigma(x)).at n=23A376256