20213

Appears in sequences

• Geometric mean of phi(n) and sigma(n) is an integer, n odd.at n=36A015705
• Number of partitions satisfying cn(0,5) < cn(1,5) + cn(4,5) + cn(2,5) and cn(0,5) < cn(1,5) + cn(4,5) + cn(3,5).at n=36A039846
• Numbers n such that n through n+5 have the same number of distinct prime factors.at n=23A045934
• a(n) = A001541(n)*A001653(n+1)*A002315(n).at n=2A111647
• Least k such that the cyclotomic polynomial Phi(k,x) contains n or -n as a coefficient, where k is restricted to be the product of 3 distinct prime numbers.at n=7A134518
• Least k such that the cyclotomic polynomial Phi(k,x) contains n or -n as a coefficient, where k is restricted to be the product of 3 distinct prime numbers.at n=8A134518
• Primitive subsequence of A111105.at n=34A137559
• Numbers k = p*q*r, with odd primes p < q < r, such that Sister Beiter's cyclotomic coefficient conjecture is false.at n=0A146961
• The odd composites c such that c=q*g*j*y/2 and q+g=j*y where q,g,j,y are distinct primes.at n=34A167629
• For any number n take the polynomial formed by the product of the terms (x-pi), where pi's are the prime factors of n. Then calculate the area between the minimum and the maximum value of the prime factors. This sequence lists the numbers for which the area is equal to zero.at n=40A203614
• 50k^2-40k-17 interleaved with 50k^2+10k+13 for k=>0.at n=41A217893
• Composite squarefree numbers k such that the arithmetic mean of the distinct prime factors of k is a prime p, and p divides k.at n=31A229094
• Number of partitions p of n such that (sum of parts with multiplicity 1) <= (sum of all other parts).at n=40A240449
• Number of (n+2)X(2+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 0 1 or 4.at n=4A252287
• Number of (n+2)X(5+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 0 1 or 4.at n=1A252290
• T(n,k)=Number of (n+2)X(k+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 0 1 or 4.at n=16A252293
• T(n,k)=Number of (n+2)X(k+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 0 1 or 4.at n=19A252293
• Products of three distinct primes that form an arithmetic progression.at n=21A262723
• Fixed points of A275957; numbers n for which A060125(n) = A225901(n).at n=45A275843
• Numbers of the form HMMSS with primes H < 24 and MM, SS < 60, for which the number of seconds after midnight, 3600*H+60*MM+SS, is also prime.at n=1A295011