1971821 has 4 divisors (see below), whose sum is σ = 1975392. Its totient is φ = 1968252.

The previous prime is 1971799. The next prime is 1971829. The reversal of 1971821 is 1281791.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1971821 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1971829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 761 + ... + 2126.

It is an arithmetic number, because the mean of its divisors is an integer number (493848).

2^1971821 is an apocalyptic number.

It is an amenable number.

1971821 is a deficient number, since it is larger than the sum of its proper divisors (3571).

1971821 is an equidigital number, since it uses as much as digits as its factorization.

1971821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3570.

The product of its digits is 1008, while the sum is 29.

The square root of 1971821 is about 1404.2154393112. The cubic root of 1971821 is about 125.3975820871.

The spelling of 1971821 in words is "one million, nine hundred seventy-one thousand, eight hundred twenty-one".