Number of the day: 668

Christian Goldbach was born on this day 331 years ago.

Properties of the number 668:

668 = 2² × 167 is the 546^th composite number and is not squarefree.
668 has 2 distinct prime factors, 6 divisors, 9 antidivisors and 332 totatives.
668 has an oblong digit sum 20 in base 10.
668 has sum of divisors equal to 1176 which is a triangular number.
Reversing the decimal digits of 668 results in a semiprime.
668 = 168² - 166² is the difference of 2 nonnegative squares in 1 way.
668 is the difference of 2 positive pentagonal numbers in 1 way.
668 is not the sum of 3 positive squares.
668² is the sum of 3 positive squares.
668 is a proper divisor of 1669² - 1.
668 is palindromic in (at least) the following bases: 18, 23, and -29.
668 in base 3 = 220202 and consists of only the digits '0' and '2'.
668 in base 9 = 822 and consists of only the digits '2' and '8'.
668 consists of only the digits '6' and '8'.
668 in base 11 = 558 and consists of only the digits '5' and '8'.
668 in base 17 = 255 and consists of only the digits '2' and '5'.
668 in base 18 = 212 and consists of only the digits '1' and '2'.
668 in base 22 = 188 and consists of only the digits '1' and '8'.
668 in base 23 = 161 and consists of only the digits '1' and '6'.
668 in base 25 = 11i and consists of only the digits '1' and 'i'.

The number 668 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A000009: Expansion of Product_{m >= 1} (1 + x^m); number of partitions of n into distinct parts; number of partitions of n into odd parts.
A005823: Numbers whose ternary expansion contains no 1's.
A026769: Triangular array T read by rows: T(n,0)=T(n,n)=1 for n >= 0; T(2,1)=2; for n >= 3 and 1<=k<=n-1, T(n,k) = T(n-1,k-1) + T(n-2,k-1) + T(n-1,k) if 1<=k<=(n-1)/2, else T(n,k) = T(n-1,k-1) + T(n-1,k).
A051225: Numbers m such that the Bernoulli number B_{2*m} has denominator 30.
A051226: Numbers m such that the Bernoulli number B_m has denominator 30.
A080054: G.f.: Product_{n >= 0} (1+x^(2n+1))/(1-x^(2n+1)).
A143823: Number of subsets {x(1),x(2),...,x(k)} of {1,2,...,n} such that all differences |x(i)-x(j)| are distinct.
A161330: Snowflake (or E-toothpick) sequence (see Comments lines for definition).
A161424: Numbers k whose largest divisor <= sqrt(k) equals 4.
A235229: Numbers whose sum of digits is 20.