21640505 has 8 divisors (see below), whose sum is σ = 26030400. Its totient is φ = 17271216.

The previous prime is 21640501. The next prime is 21640513. The reversal of 21640505 is 50504612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21640505 - 2² = 21640501 is a prime.

It is a super-2 number, since 2×21640505² = 936622913310050, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21640501) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2735 + ... + 7124.

It is an arithmetic number, because the mean of its divisors is an integer number (3253800).

Almost surely, 2^21640505 is an apocalyptic number.

It is an amenable number.

21640505 is a deficient number, since it is larger than the sum of its proper divisors (4389895).

21640505 is an equidigital number, since it uses as much as digits as its factorization.

21640505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10303.

The product of its (nonzero) digits is 1200, while the sum is 23.

The square root of 21640505 is about 4651.9356186431. The cubic root of 21640505 is about 278.6693023860.

The spelling of 21640505 in words is "twenty-one million, six hundred forty thousand, five hundred five".