1977821 has 2 divisors, whose sum is σ = 1977822. Its totient is φ = 1977820.

The previous prime is 1977817. The next prime is 1977823. The reversal of 1977821 is 1287791.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1792921 + 184900 = 1339^2 + 430^2 .

It is a cyclic number.

It is not a de Polignac number, because 1977821 - 2² = 1977817 is a prime.

It is a Sophie Germain prime.

Together with 1977823, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1977823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 988910 + 988911.

It is an arithmetic number, because the mean of its divisors is an integer number (988911).

2^1977821 is an apocalyptic number.

It is an amenable number.

1977821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1977821 is an equidigital number, since it uses as much as digits as its factorization.

1977821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7056, while the sum is 35.

The square root of 1977821 is about 1406.3502408717. The cubic root of 1977821 is about 125.5246429178.

The spelling of 1977821 in words is "one million, nine hundred seventy-seven thousand, eight hundred twenty-one".