21621593 has 6 divisors (see below), whose sum is σ = 25151706. Its totient is φ = 18532752.

The previous prime is 21621577. The next prime is 21621629. The reversal of 21621593 is 39512612.

It can be written as a sum of positive squares in only one way, i.e., 21603904 + 17689 = 4648^2 + 133^2 .

It is not a de Polignac number, because 21621593 - 2⁴ = 21621577 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21621293) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 220580 + ... + 220677.

It is an arithmetic number, because the mean of its divisors is an integer number (4191951).

Almost surely, 2^21621593 is an apocalyptic number.

It is an amenable number.

21621593 is a deficient number, since it is larger than the sum of its proper divisors (3530113).

21621593 is an equidigital number, since it uses as much as digits as its factorization.

21621593 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 441271 (or 441264 counting only the distinct ones).

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

The square root of 21621593 is about 4649.9024720955. The cubic root of 21621593 is about 278.5881008024.

The spelling of 21621593 in words is "twenty-one million, six hundred twenty-one thousand, five hundred ninety-three".