21543931 has 2 divisors, whose sum is σ = 21543932. Its totient is φ = 21543930.

The previous prime is 21543923. The next prime is 21543961. The reversal of 21543931 is 13934512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21543931 - 2³ = 21543923 is a prime.

It is a super-2 number, since 2×21543931² = 928281925865522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21543931.

It is not a weakly prime, because it can be changed into another prime (21543911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771965 + 10771966.

It is an arithmetic number, because the mean of its divisors is an integer number (10771966).

Almost surely, 2^21543931 is an apocalyptic number.

21543931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21543931 is an equidigital number, since it uses as much as digits as its factorization.

21543931 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 28.

The square root of 21543931 is about 4641.5440318928. The cubic root of 21543931 is about 278.2541496895.

The spelling of 21543931 in words is "twenty-one million, five hundred forty-three thousand, nine hundred thirty-one".