198 (number)

198 (one hundred [and] ninety-eight) is the natural number following 197 and preceding 199.

In mathematics

• 198 is the number of nonzero palindromes less than 10⁴.
• 198 is the sum of products of terms in all partitions of the number 9.
• 198 is the smallest number that can be written as a sum of four positive squares in ten different ways: 198 = 1² + 2² + 7² + 12² = 1² + 4² + 9² + 10² = 2² + 3² + 4² + 13² = 2² + 3² + 8² + 11² = 2² + 5² + 5² + 12² = 2² + 7² + 8² + 9² = 3² + 3² + 6² + 12² = 3² + 5² + 8² + 10² = 4² + 5² + 6² + 11² = 6² + 7² + 7² + 8².
• 198 is a companion Pell number. Its corresponding Pell number is 70.
• 198 is the 4th term of the sequence a(n) = 10*a(n-1) - a(n-2) with a(0) = 0, a(1) = 2. This sequence has the property that for each n, if A = a(n), B = 2*a(n+1), C = 3*a(n+1) then A*B+1, A*C+1, B*C+1 are perfect squares.
• 198 is the first number between a twin prime pair such that product of itself by its reversal (198 x 891 = 176418) is also between a twin prime pair.
• 198 is a Harshad number, which means it is divisible by the sum of its digits.
• 198 is both the average of a twin prime pair (197, 199), and the sum of 2 successive primes (97, 101).
• 198 is a coordination number for hexagonal lattices, which means it is the difference between two consecutive centered hexagonal numbers. In this case, 198 is the difference between 3367 and 3169 (34th and 33rd centered hexagonal numbers), so the hexagonal spatial arrangement of 3367 has 198 dots in the border.
• 198 is also the 8th coordination number for cubic lattices, making it the 6th number to be part of the coordination sequences for both cubic and hexagonal lattices.

In other fields

198 is also:

• The State Highway Police emergency telephone number in Brazil .

• The number of ridges on a U.S. dollar coin.

See also

• The year AD 198 or 198 BC
• X-Men: The 198