21555001 has 16 divisors (see below), whose sum is σ = 23889600. Its totient is φ = 19326528.

The previous prime is 21554993. The next prime is 21555007. The reversal of 21555001 is 10055512.

It is not a de Polignac number, because 21555001 - 2³ = 21554993 is a prime.

It is a super-2 number, since 2×21555001² = 929236136220002, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21555001.

It is not an unprimeable number, because it can be changed into a prime (21555007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 120330 + ... + 120508.

It is an arithmetic number, because the mean of its divisors is an integer number (1493100).

Almost surely, 2^21555001 is an apocalyptic number.

It is an amenable number.

21555001 is a deficient number, since it is larger than the sum of its proper divisors (2334599).

21555001 is a wasteful number, since it uses less digits than its factorization.

21555001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 408.

The product of its (nonzero) digits is 250, while the sum is 19.

The square root of 21555001 is about 4642.7363698578. The cubic root of 21555001 is about 278.3018003249.

The spelling of 21555001 in words is "twenty-one million, five hundred fifty-five thousand, one".