20921217 has 4 divisors (see below), whose sum is σ = 27894960. Its totient is φ = 13947476.

The previous prime is 20921161. The next prime is 20921221. The reversal of 20921217 is 71212902.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20921217 - 2¹¹ = 20919169 is a prime.

It is a super-2 number, since 2×20921217² = 875394641522178, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20921227) 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, 3486867 + ... + 3486872.

It is an arithmetic number, because the mean of its divisors is an integer number (6973740).

Almost surely, 2^20921217 is an apocalyptic number.

It is an amenable number.

20921217 is a deficient number, since it is larger than the sum of its proper divisors (6973743).

20921217 is an equidigital number, since it uses as much as digits as its factorization.

20921217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6973742.

The product of its (nonzero) digits is 504, while the sum is 24.

The square root of 20921217 is about 4573.9716877130. The cubic root of 20921217 is about 275.5469752563.

The spelling of 20921217 in words is "twenty million, nine hundred twenty-one thousand, two hundred seventeen".