55154

Appears in sequences

• a(n) = Sum_{k=1..n-1} k*sigma(k)*sigma(n-k).at n=22A000441
• 4-dimensional figurate numbers: a(n) = (5*n-1)*binomial(n+2,3)/4.at n=22A002418
• Numbers k such that usigma(k) = phi(k)*omega(k), where omega(k) is the number of distinct prime divisors of k.at n=23A063795
• Numbers n such that the arithmetic, geometric and harmonic means of phi(n) and sigma(n) are all integers.at n=24A065146
• Numbers k such that sigma(k) = bigomega(k) * phi(k).at n=19A067238
• Numbers k such that sigma(k) = 4*phi(k).at n=18A068390
• Numbers k such that sigma(k) = phi(k*bigomega(k)).at n=19A068400
• Number of nonisomorphic unrooted unicursal planar maps with n edges.at n=8A069730
• Numbers k such that sigma(k) = phi(k)*omega(k).at n=13A073567
• Group the natural numbers such that the n-th group sum is divisible by prime(n): (1, 2, 3), (4, 5), (6, 7, 8, 9), (10, 11), (12, 13, 14, 15, 16, 17, 18, 19, 20, 21), ... Sequence contains the sum of the terms in the n-th group.at n=28A086491
• a(n) = binomial(floor(n/2),4) + (ceiling(n/2)-3)*binomial(floor(n/2),3).at n=49A234277
• a(n) = n*(n+1)*(n+2)*(n^2+2*n+17)/120.at n=21A257199
• Expansion of x*(1 + 3*x + x^2)/((1 - x)^5*(1 + x)^4).at n=43A287143
• Integers n such that sigma(n)/phi(n) is a perfect square.at n=35A293391
• a(n) = 384*4^n - 576*3^n + 220*2^n - 14.at n=4A305862
• Array read by ascending antidiagonals: A(n, k) = n!*[x^n] Li(-k, 1 - exp(-4*x))/(4*sinh(x)), where Li(n, z) is the polylogarithm function.at n=32A345394