20555621021 has 4 divisors (see below), whose sum is σ = 22136822652. Its totient is φ = 18974419392.

The previous prime is 20555620997. The next prime is 20555621039. The reversal of 20555621021 is 12012655502.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12012655502 = 2 ⋅6006327751.

It can be written as a sum of positive squares in 2 ways, for example, as 14153860900 + 6401760121 = 118970^2 + 80011^2 .

It is a cyclic number.

It is not a de Polignac number, because 20555621021 - 2¹⁸ = 20555358877 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20555624021) 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, 790600796 + ... + 790600821.

It is an arithmetic number, because the mean of its divisors is an integer number (5534205663).

Almost surely, 2^20555621021 is an apocalyptic number.

It is an amenable number.

20555621021 is a deficient number, since it is larger than the sum of its proper divisors (1581201631).

20555621021 is a wasteful number, since it uses less digits than its factorization.

20555621021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1581201630.

The product of its (nonzero) digits is 6000, while the sum is 29.

The spelling of 20555621021 in words is "twenty billion, five hundred fifty-five million, six hundred twenty-one thousand, twenty-one".