21028190121 has 9 divisors (see below), whose sum is σ = 30374680791. Its totient is φ = 14018503392.

The previous prime is 21028190107. The next prime is 21028190123. The reversal of 21028190121 is 12109182012.

The square root of 21028190121 is 145011.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 18204755625 + 2823434496 = 134925^2 + 53136^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 21028190121 - 2⁷ = 21028189993 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21028190123) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 410865 + ... + 459201.

Almost surely, 2^21028190121 is an apocalyptic number.

21028190121 is the 145011-st square number.

21028190121 is the 72506-th centered octagonal number.

It is an amenable number.

21028190121 is a deficient number, since it is larger than the sum of its proper divisors (9346490670).

21028190121 is an frugal number, since it uses more digits than its factorization.

21028190121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 96680 (or 48340 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 27.

Multiplying 21028190121 by its product of nonzero digits (576), we get a square (12112237509696 = 3480264²).

The spelling of 21028190121 in words is "twenty-one billion, twenty-eight million, one hundred ninety thousand, one hundred twenty-one".