20987206921 has 2 divisors, whose sum is σ = 20987206922. Its totient is φ = 20987206920.

The previous prime is 20987206883. The next prime is 20987206991. The reversal of 20987206921 is 12960278902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13670286400 + 7316920521 = 116920^2 + 85539^2 .

It is a cyclic number.

It is not a de Polignac number, because 20987206921 - 2²³ = 20978818313 is a prime.

It is not a weakly prime, because it can be changed into another prime (20987206991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10493603460 + 10493603461.

It is an arithmetic number, because the mean of its divisors is an integer number (10493603461).

Almost surely, 2^20987206921 is an apocalyptic number.

It is an amenable number.

20987206921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20987206921 is an equidigital number, since it uses as much as digits as its factorization.

20987206921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 217728, while the sum is 46.

The spelling of 20987206921 in words is "twenty billion, nine hundred eighty-seven million, two hundred six thousand, nine hundred twenty-one".