21947787 has 16 divisors (see below), whose sum is σ = 32721280. Its totient is φ = 14539176.

The previous prime is 21947747. The next prime is 21947791. The reversal of 21947787 is 78774912.

It is a happy number.

It is not a de Polignac number, because 21947787 - 2⁸ = 21947531 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21947707) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1908 + ... + 6894.

It is an arithmetic number, because the mean of its divisors is an integer number (2045080).

Almost surely, 2^21947787 is an apocalyptic number.

21947787 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21947787 is a deficient number, since it is larger than the sum of its proper divisors (10773493).

21947787 is a wasteful number, since it uses less digits than its factorization.

21947787 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5159 (or 5153 counting only the distinct ones).

The product of its digits is 197568, while the sum is 45.

The square root of 21947787 is about 4684.8465289698. The cubic root of 21947787 is about 279.9820864390.

The spelling of 21947787 in words is "twenty-one million, nine hundred forty-seven thousand, seven hundred eighty-seven".