21731247 has 24 divisors (see below), whose sum is σ = 33445776. Its totient is φ = 14090112.

The previous prime is 21731243. The next prime is 21731257. The reversal of 21731247 is 74213712.

It is a happy number.

It is not a de Polignac number, because 21731247 - 2² = 21731243 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21731247.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731243) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7783 + ... + 10199.

It is an arithmetic number, because the mean of its divisors is an integer number (1393574).

Almost surely, 2^21731247 is an apocalyptic number.

21731247 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21731247 is a deficient number, since it is larger than the sum of its proper divisors (11714529).

21731247 is an equidigital number, since it uses as much as digits as its factorization.

21731247 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2469 (or 2457 counting only the distinct ones).

The product of its digits is 2352, while the sum is 27.

The square root of 21731247 is about 4661.6785603471. The cubic root of 21731247 is about 279.0582604659.

Adding to 21731247 its reverse (74213712), we get a palindrome (95944959).

The spelling of 21731247 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred forty-seven".