21551605 has 16 divisors (see below), whose sum is σ = 27676800. Its totient is φ = 16061760.

The previous prime is 21551591. The next prime is 21551623. The reversal of 21551605 is 50615512.

It is not a de Polignac number, because 21551605 - 2⁵ = 21551573 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21551605.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3936 + ... + 7654.

It is an arithmetic number, because the mean of its divisors is an integer number (1729800).

Almost surely, 2^21551605 is an apocalyptic number.

It is an amenable number.

21551605 is a deficient number, since it is larger than the sum of its proper divisors (6125195).

21551605 is a wasteful number, since it uses less digits than its factorization.

21551605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3804.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21551605 is about 4642.3706228607. The cubic root of 21551605 is about 278.2871840331.

The spelling of 21551605 in words is "twenty-one million, five hundred fifty-one thousand, six hundred five".