21978429 has 8 divisors (see below), whose sum is σ = 31968672. Its totient is φ = 13320240.

The previous prime is 21978403. The next prime is 21978487. The reversal of 21978429 is 92487912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21978429 - 2⁷ = 21978301 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979429) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 332974 + ... + 333039.

It is an arithmetic number, because the mean of its divisors is an integer number (3996084).

Almost surely, 2^21978429 is an apocalyptic number.

It is an amenable number.

21978429 is a deficient number, since it is larger than the sum of its proper divisors (9990243).

21978429 is a wasteful number, since it uses less digits than its factorization.

21978429 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 666027.

The product of its digits is 72576, while the sum is 42.

The square root of 21978429 is about 4688.1157195615. The cubic root of 21978429 is about 280.1123231324.

It can be divided in two parts, 219784 and 29, that multiplied together give a palindrome (6373736).

The spelling of 21978429 in words is "twenty-one million, nine hundred seventy-eight thousand, four hundred twenty-nine".