21740247 has 12 divisors (see below), whose sum is σ = 31801120. Its totient is φ = 14309568.

The previous prime is 21740239. The next prime is 21740249. The reversal of 21740247 is 74204712.

It is a happy number.

21740247 is a `hidden beast` number, since 217 + 402 + 47 = 666.

It is not a de Polignac number, because 21740247 - 2³ = 21740239 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21740247.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21740249) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14578 + ... + 15999.

Almost surely, 2^21740247 is an apocalyptic number.

21740247 is a deficient number, since it is larger than the sum of its proper divisors (10060873).

21740247 is a wasteful number, since it uses less digits than its factorization.

21740247 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30662 (or 30659 counting only the distinct ones).

The product of its (nonzero) digits is 3136, while the sum is 27.

The square root of 21740247 is about 4662.6437779440. The cubic root of 21740247 is about 279.0967791591.

Adding to 21740247 its reverse (74204712), we get a palindrome (95944959).

The spelling of 21740247 in words is "twenty-one million, seven hundred forty thousand, two hundred forty-seven".