21555001543 has 4 divisors (see below), whose sum is σ = 21555698968. Its totient is φ = 21554304120.

The previous prime is 21555001519. The next prime is 21555001553. The reversal of 21555001543 is 34510055512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21555001543 - 2⁹ = 21555001031 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555001553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 300093 + ... + 364918.

It is an arithmetic number, because the mean of its divisors is an integer number (5388924742).

Almost surely, 2^21555001543 is an apocalyptic number.

21555001543 is a deficient number, since it is larger than the sum of its proper divisors (697425).

21555001543 is an equidigital number, since it uses as much as digits as its factorization.

21555001543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 697424.

The product of its (nonzero) digits is 15000, while the sum is 31.

The spelling of 21555001543 in words is "twenty-one billion, five hundred fifty-five million, one thousand, five hundred forty-three".