21428621 has 2 divisors, whose sum is σ = 21428622. Its totient is φ = 21428620.

The previous prime is 21428611. The next prime is 21428681. The reversal of 21428621 is 12682412.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17547721 + 3880900 = 4189^2 + 1970^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21428621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21428611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10714310 + 10714311.

It is an arithmetic number, because the mean of its divisors is an integer number (10714311).

Almost surely, 2^21428621 is an apocalyptic number.

It is an amenable number.

21428621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21428621 is an equidigital number, since it uses as much as digits as its factorization.

21428621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1536, while the sum is 26.

The square root of 21428621 is about 4629.1058531859. The cubic root of 21428621 is about 277.7568263250.

The spelling of 21428621 in words is "twenty-one million, four hundred twenty-eight thousand, six hundred twenty-one".