83720

Appears in sequences

• Numbers k such that sigma(k+1) = 5*phi(k).at n=10A067263
• Amicable triples: numbers such that sigma(x) = sigma(y) = sigma(z) = x+y+z, x<y<z. We order these triples according to the common value of sigma. Sequence gives y numbers.at n=14A125491
• Sums of the products of n consecutive pairs of numbers.at n=39A135036
• Numbers n such that product of double factorials of the digits of n equals sigma(n).at n=19A158989
• Triangle T(n,k) = (-1)^(k+n)*A054655(n,n-k), 0<=k<n, read by rows.at n=41A177938
• Number of increasing sequences of n integers x(1),...,x(n) with values in 1..4*n such that x(j) divides x(k) if j divides k.at n=15A180386
• Number of (n+1)X2 0..3 arrays with rows and columns of permanents of all 2X2 subblocks lexicographically nondecreasing, and all 2X2 permanents nonzero.at n=3A205194
• Number of (n+1)X5 0..3 arrays with rows and columns of permanents of all 2X2 subblocks lexicographically nondecreasing, and all 2X2 permanents nonzero.at n=0A205197
• T(n,k)=Number of (n+1)X(k+1) 0..3 arrays with rows and columns of permanents of all 2X2 subblocks lexicographically nondecreasing, and all 2X2 permanents nonzero.at n=6A205198
• T(n,k)=Number of (n+1)X(k+1) 0..3 arrays with rows and columns of permanents of all 2X2 subblocks lexicographically nondecreasing, and all 2X2 permanents nonzero.at n=9A205198
• GCD of A002443(n) and A002444(n), numerator and denominator in Feinler's formula for the Bernoulli number B_{2n}.at n=44A266911
• a(1) = 1; a(n+1) = Sum_{d|n} sigma(n/d)*a(d), where sigma = sum of divisors (A000203).at n=48A307817
• Numbers k such that k and k+1 have at least 4 but not both exactly 4 distinct prime factors.at n=17A321494
• a(n) = Sum_{1 <= i <= j <= k <= m <= n} gcd(i,j,k,m).at n=34A344992
• a(n) is the least practical number A005153(k) such that A005153(k+1) - A005153(k) = 2*n, or -1 if no such number exists.at n=16A364707