21717207 has 8 divisors (see below), whose sum is σ = 32173680. Its totient is φ = 14478120.

The previous prime is 21717203. The next prime is 21717217. The reversal of 21717207 is 70271712.

It is not a de Polignac number, because 21717207 - 2² = 21717203 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 804341 = 21717207 / (2 + 1 + 7 + 1 + 7 + 2 + 0 + 7).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21717203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 402144 + ... + 402197.

It is an arithmetic number, because the mean of its divisors is an integer number (4021710).

Almost surely, 2^21717207 is an apocalyptic number.

21717207 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21717207 is a deficient number, since it is larger than the sum of its proper divisors (10456473).

21717207 is an equidigital number, since it uses as much as digits as its factorization.

21717207 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 804350 (or 804344 counting only the distinct ones).

The product of its (nonzero) digits is 1372, while the sum is 27.

The square root of 21717207 is about 4660.1724217029. The cubic root of 21717207 is about 278.9981500629.

Adding to 21717207 its reverse (70271712), we get a palindrome (91988919).

It can be divided in two parts, 217 and 17207, that added together give a square (17424 = 132²).

The spelling of 21717207 in words is "twenty-one million, seven hundred seventeen thousand, two hundred seven".