21137647 has 4 divisors (see below), whose sum is σ = 22381056. Its totient is φ = 19894240.

The previous prime is 21137609. The next prime is 21137657. The reversal of 21137647 is 74673112.

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

It is a cyclic number.

It is not a de Polignac number, because 21137647 - 2¹⁵ = 21104879 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21137657) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 621679 + ... + 621712.

It is an arithmetic number, because the mean of its divisors is an integer number (5595264).

Almost surely, 2^21137647 is an apocalyptic number.

21137647 is a deficient number, since it is larger than the sum of its proper divisors (1243409).

21137647 is a wasteful number, since it uses less digits than its factorization.

21137647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1243408.

The product of its digits is 7056, while the sum is 31.

The square root of 21137647 is about 4597.5696840831. The cubic root of 21137647 is about 276.4938952923.

The spelling of 21137647 in words is "twenty-one million, one hundred thirty-seven thousand, six hundred forty-seven".