21125639 has 2 divisors, whose sum is σ = 21125640. Its totient is φ = 21125638.

The previous prime is 21125633. The next prime is 21125647. The reversal of 21125639 is 93652112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21125639 - 2⁴ = 21125623 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21125633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10562819 + 10562820.

It is an arithmetic number, because the mean of its divisors is an integer number (10562820).

Almost surely, 2^21125639 is an apocalyptic number.

21125639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21125639 is an equidigital number, since it uses as much as digits as its factorization.

21125639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 29.

The square root of 21125639 is about 4596.2635912228. The cubic root of 21125639 is about 276.4415279435.

The spelling of 21125639 in words is "twenty-one million, one hundred twenty-five thousand, six hundred thirty-nine".