1820 has 24 divisors (see below), whose sum is σ = 4704. Its totient is φ = 576.

The previous prime is 1811. The next prime is 1823. The reversal of 1820 is 281.

1820 = 13² + 14² + ... + 19².

1820 is nontrivially palindromic in base 9.

1820 is an esthetic number in base 8, because in such base its adjacent digits differ by 1.

1820 is a nontrivial binomial coefficient, being equal to C(16, 4).

1820 is an undulating number in base 8.

It is a nialpdrome in base 7, base 13 and base 14.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1823) by changing a digit.

1820 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 134 + ... + 146.

It is an arithmetic number, because the mean of its divisors is an integer number (196).

2¹⁸²⁰ is an apocalyptic number.

1820 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

1820 is the 35-th pentagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2352).

1820 is an abundant number, since it is smaller than the sum of its proper divisors (2884).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1820 is a wasteful number, since it uses less digits than its factorization.

1820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29 (or 27 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 1820 is about 42.6614580154. The cubic root of 1820 is about 12.2092914975.

The spelling of 1820 in words is "one thousand, eight hundred twenty".