21729396 has 24 divisors (see below), whose sum is σ = 54602464. Its totient is φ = 6685920.

The previous prime is 21729391. The next prime is 21729403. The reversal of 21729396 is 69392712.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21729391) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 69490 + ... + 69801.

Almost surely, 2^21729396 is an apocalyptic number.

21729396 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

21729396 is an abundant number, since it is smaller than the sum of its proper divisors (32873068).

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

21729396 is a wasteful number, since it uses less digits than its factorization.

21729396 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139311 (or 139309 counting only the distinct ones).

The product of its digits is 40824, while the sum is 39.

The square root of 21729396 is about 4661.4800224821. The cubic root of 21729396 is about 279.0503371362.

The spelling of 21729396 in words is "twenty-one million, seven hundred twenty-nine thousand, three hundred ninety-six".