821511887821 has 2 divisors, whose sum is σ = 821511887822. Its totient is φ = 821511887820.

The previous prime is 821511887797. The next prime is 821511887837. The reversal of 821511887821 is 128788115128.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 701764745796 + 119747142025 = 837714^2 + 346045^2 .

It is a cyclic number.

It is not a de Polignac number, because 821511887821 - 2⁹ = 821511887309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (821511887621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410755943910 + 410755943911.

It is an arithmetic number, because the mean of its divisors is an integer number (410755943911).

Almost surely, 2^821511887821 is an apocalyptic number.

It is an amenable number.

821511887821 is a deficient number, since it is larger than the sum of its proper divisors (1).

821511887821 is an equidigital number, since it uses as much as digits as its factorization.

821511887821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 573440, while the sum is 52.

The spelling of 821511887821 in words is "eight hundred twenty-one billion, five hundred eleven million, eight hundred eighty-seven thousand, eight hundred twenty-one".