21638402 has 4 divisors (see below), whose sum is σ = 32457606. Its totient is φ = 10819200.

The previous prime is 21638401. The next prime is 21638431. The reversal of 21638402 is 20483612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 12752041 + 8886361 = 3571^2 + 2981^2 .

It is a super-2 number, since 2×21638402² = 936440882227208, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21638401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5409599 + ... + 5409602.

Almost surely, 2^21638402 is an apocalyptic number.

21638402 is a deficient number, since it is larger than the sum of its proper divisors (10819204).

21638402 is a wasteful number, since it uses less digits than its factorization.

21638402 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10819203.

The product of its (nonzero) digits is 2304, while the sum is 26.

The square root of 21638402 is about 4651.7095782089. The cubic root of 21638402 is about 278.6602751702.

The spelling of 21638402 in words is "twenty-one million, six hundred thirty-eight thousand, four hundred two".