21870729 has 28 divisors (see below), whose sum is σ = 34538800. Its totient is φ = 13804344.

The previous prime is 21870713. The next prime is 21870733. The reversal of 21870729 is 92707812.

It is not a de Polignac number, because 21870729 - 2⁴ = 21870713 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21870693 and 21870702.

It is not an unprimeable number, because it can be changed into a prime (21870029) by changing a digit.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 13062 + ... + 14640.

Almost surely, 2^21870729 is an apocalyptic number.

It is an amenable number.

21870729 is a deficient number, since it is larger than the sum of its proper divisors (12668071).

21870729 is an equidigital number, since it uses as much as digits as its factorization.

21870729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1616 (or 1601 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 21870729 is about 4676.6151220728. The cubic root of 21870729 is about 279.6540327338.

The spelling of 21870729 in words is "twenty-one million, eight hundred seventy thousand, seven hundred twenty-nine".