21628121 has 2 divisors, whose sum is σ = 21628122. Its totient is φ = 21628120.

The previous prime is 21628031. The next prime is 21628127. The reversal of 21628121 is 12182612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17547721 + 4080400 = 4189^2 + 2020^2 .

It is a cyclic number.

It is not a de Polignac number, because 21628121 - 2²² = 17433817 is a prime.

It is not a weakly prime, because it can be changed into another prime (21628127) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10814060 + 10814061.

It is an arithmetic number, because the mean of its divisors is an integer number (10814061).

Almost surely, 2^21628121 is an apocalyptic number.

It is an amenable number.

21628121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21628121 is an equidigital number, since it uses as much as digits as its factorization.

21628121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 384, while the sum is 23.

The square root of 21628121 is about 4650.6043693266. The cubic root of 21628121 is about 278.6161351247.

The spelling of 21628121 in words is "twenty-one million, six hundred twenty-eight thousand, one hundred twenty-one".