21987747 has 16 divisors (see below), whose sum is σ = 33991680. Its totient is φ = 14020776.

The previous prime is 21987737. The next prime is 21987787. The reversal of 21987747 is 74778912.

It is a happy number.

It is not a de Polignac number, because 21987747 - 2⁷ = 21987619 is a prime.

It is a super-2 number, since 2×21987747² = 966922036272018, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21987727) 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, 17083 + ... + 18324.

It is an arithmetic number, because the mean of its divisors is an integer number (2124480).

Almost surely, 2^21987747 is an apocalyptic number.

21987747 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21987747 is a deficient number, since it is larger than the sum of its proper divisors (12003933).

21987747 is a wasteful number, since it uses less digits than its factorization.

21987747 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35439 (or 35433 counting only the distinct ones).

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

The square root of 21987747 is about 4689.1094037141. The cubic root of 21987747 is about 280.1519031202.

The spelling of 21987747 in words is "twenty-one million, nine hundred eighty-seven thousand, seven hundred forty-seven".