21507943 has 4 divisors (see below), whose sum is σ = 22639960. Its totient is φ = 20375928.

The previous prime is 21507931. The next prime is 21507947. The reversal of 21507943 is 34970512.

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 21507943 - 2⁵ = 21507911 is a prime.

It is a super-2 number, since 2×21507943² = 925183224182498, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21507947) 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 3 ways as a sum of consecutive naturals, for example, 565980 + ... + 566017.

It is an arithmetic number, because the mean of its divisors is an integer number (5659990).

Almost surely, 2^21507943 is an apocalyptic number.

21507943 is a deficient number, since it is larger than the sum of its proper divisors (1132017).

21507943 is a wasteful number, since it uses less digits than its factorization.

21507943 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1132016.

The product of its (nonzero) digits is 7560, while the sum is 31.

The square root of 21507943 is about 4637.6656843718. The cubic root of 21507943 is about 278.0991270466.

The spelling of 21507943 in words is "twenty-one million, five hundred seven thousand, nine hundred forty-three".