21729456 has 60 divisors (see below), whose sum is σ = 69502992. Its totient is φ = 6208128.

The previous prime is 21729427. The next prime is 21729469. The reversal of 21729456 is 65492712.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21729456.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9771 + ... + 11786.

Almost surely, 2^21729456 is an apocalyptic number.

It is an amenable number.

21729456 is an abundant number, since it is smaller than the sum of its proper divisors (47773536).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21729456 is a wasteful number, since it uses less digits than its factorization.

21729456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21578 (or 21569 counting only the distinct ones).

The product of its digits is 30240, while the sum is 36.

The square root of 21729456 is about 4661.4864582019. The cubic root of 21729456 is about 279.0505939773.

It can be divided in two parts, 2172 and 9456, that added together give a triangular number (11628 = T₁₅₂).

The spelling of 21729456 in words is "twenty-one million, seven hundred twenty-nine thousand, four hundred fifty-six".