21328537 has 2 divisors, whose sum is σ = 21328538. Its totient is φ = 21328536.

The previous prime is 21328501. The next prime is 21328561. The reversal of 21328537 is 73582312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15452761 + 5875776 = 3931^2 + 2424^2 .

It is a cyclic number.

It is not a de Polignac number, because 21328537 - 2⁷ = 21328409 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21328499 and 21328508.

It is not a weakly prime, because it can be changed into another prime (21328597) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10664268 + 10664269.

It is an arithmetic number, because the mean of its divisors is an integer number (10664269).

Almost surely, 2^21328537 is an apocalyptic number.

It is an amenable number.

21328537 is a deficient number, since it is larger than the sum of its proper divisors (1).

21328537 is an equidigital number, since it uses as much as digits as its factorization.

21328537 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10080, while the sum is 31.

The square root of 21328537 is about 4618.2829060160. The cubic root of 21328537 is about 277.3237232337.

The spelling of 21328537 in words is "twenty-one million, three hundred twenty-eight thousand, five hundred thirty-seven".