Number of the day: 6440

Properties of the number 6440:

6440 = 2³ × 5 × 7 × 23 is the 5603^th composite number and is not squarefree.
6440 has 4 distinct prime factors, 32 divisors, 19 antidivisors and 2112 totatives.
6440 has a semiprime digit sum 14 in base 10.
6440 = (20 × 21)/2 + … + (35 × 36)/2 is the sum of at least 2 consecutive triangular numbers in 1 way.
6440 = 1611² - 1609² = 807² - 803² = 327² - 317² = 237² - 223² = 171² - 151² = 129² - 101² = 93² - 47² = 81² - 11² is the difference of 2 nonnegative squares in 8 ways.
6440 is the difference of 2 positive pentagonal numbers in 3 ways.
6440 = 10² + 16² + 78² is the sum of 3 positive squares.
6440² = 3864² + 5152² is the sum of 2 positive squares in 1 way.
6440² is the sum of 3 positive squares.
6440 is a proper divisor of 139² - 1.
6440 is palindromic in (at least) the following bases: 21, 33, 41, 91, -19, -39, -58, and -74.
6440 in base 3 = 22211112 and consists of only the digits '1' and '2'.
6440 in base 12 = 3888 and consists of only the digits '3' and '8'.
6440 in base 21 = ece and consists of only the digits 'c' and 'e'.
6440 in base 33 = 5u5 and consists of only the digits '5' and 'u'.
6440 in base 41 = 3Y3 and consists of only the digits '3' and 'Y'.

The number 6440 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A007742: a(n) = n*(4*n+1).
A033587: a(n) = 2*n*(4*n + 3).
A045944: Rhombic matchstick numbers: a(n) = n*(3*n+2).
A078355: Minimal (positive) solution a(n) of Pell equation b(n)^2 - D(n)*a(n)^2 = +4 with D(n)= A077425(n). The companion sequence is a(n)=A077428(n).
A085146: Numbers n such that n!!!!+1 is prime.
A163934: Triangle related to the asymptotic expansion of E(x,m=4,n).
A175525: Numbers n such that n divides the sum of digits of 13^n.
A196856: T(n,k)=Number of nXk 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 3,1,0,2,4 for x=0,1,2,3,4
A234140: T(n,k)=Number of (n+1)X(k+1) 0..3 arrays with every 2X2 subblock having the sum of the absolute values of all six edge and diagonal differences equal to 9
A304638: a(n) equals the coefficient of x^n in Sum_{m>=0} (x^m + 1/x^m)^m for n > 0.