66960

Appears in sequences

• Expansion of e.g.f.: sech(log(x+1)-arctan(x))=1-3/4!*x^4+40/5!*x^5-250/6!*x^6+840/7!*x^7...at n=9A013257
• Numbers k such that the set of prime divisors of k is equal to the set of prime divisors of sigma(k).at n=23A027598
• Numbers k that divide the (left) concatenation of all numbers <= k written in base 19 (most significant digit on left).at n=54A029488
• Number of independent components for a Weyl tensor in n dimensions.at n=27A052472
• Numbers k such that (k, phi(k), sigma(k)) lies on a sphere with integral radius centered at the origin, i.e., k^2 + phi(k)^2 + sigma(k)^2 is a square.at n=7A066785
• a(n) = Z(S_m; sigma[1](n), sigma[2](n),..., sigma[m](n)) where Z(S_m; x_1,x_2,...,x_m) is the cycle index of the symmetric group S_m and sigma[k](n) is the sum of k-th powers of divisors of n; m=3.at n=23A068020
• Sum of divisors of Motzkin number A001006(n).at n=13A152981
• a(n) = (-1)^(n+1) * n*(n-1)*(n-4)*(n+1)/12.at n=29A167387
• Numbers with prime factorization pqr^3s^4.at n=21A190294
• Triangle of earliest friendly numbers having n friends.at n=21A211679
• Triangle of earliest friendly numbers having n friends.at n=28A211679
• Numbers k for which sigma(k)/k - 5/9 is an integer.at n=2A218416
• Exponential generating function = (1+x)^(1+x^2).at n=9A247212
• a(n) = n*(n+1)*(13*n+2)/6.at n=31A257093
• a(1) = 1; thereafter a(n) is the product of all 0 < m < n for which n == a(m) (mod m).at n=48A271530
• Average of amicable pairs (x,y), ordered by the smaller value x given in A002025.at n=9A275315
• Average of amicable pairs (x,y), ordered by the sum x+y given in A259953.at n=8A275316
• Numbers m that can be written as x*y with phi(x)*sigma(y) = 2*x*y, where x and y are positive integers, phi(.) is Euler's totient function and sigma(y) is the sum of all positive divisors of y.at n=43A279915
• Number of nonisomorphic proper colorings of partition multicycle graph using six colors.at n=65A298266
• Numbers k such that A048675(sigma(k)) is equal to A048675(2*k).at n=18A331751