21768388 has 6 divisors (see below), whose sum is σ = 38094686. Its totient is φ = 10884192.

The previous prime is 21768361. The next prime is 21768391. The reversal of 21768388 is 88386712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 19642624 + 2125764 = 4432^2 + 1458^2 .

It is a super-2 number, since 2×21768388² = 947725432237088, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2721045 + ... + 2721052.

Almost surely, 2^21768388 is an apocalyptic number.

It is an amenable number.

21768388 is a deficient number, since it is larger than the sum of its proper divisors (16326298).

21768388 is a wasteful number, since it uses less digits than its factorization.

21768388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5442101 (or 5442099 counting only the distinct ones).

The product of its digits is 129024, while the sum is 43.

The square root of 21768388 is about 4665.6605105815. The cubic root of 21768388 is about 279.2171500099.

The spelling of 21768388 in words is "twenty-one million, seven hundred sixty-eight thousand, three hundred eighty-eight".