212005721 has 4 divisors (see below), whose sum is σ = 212036352. Its totient is φ = 211975092.

The previous prime is 212005709. The next prime is 212005723. The reversal of 212005721 is 127500212.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 212005721 - 2¹⁸ = 211743577 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 212005693 and 212005702.

It is not an unprimeable number, because it can be changed into a prime (212005723) 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, 536 + ... + 20598.

It is an arithmetic number, because the mean of its divisors is an integer number (53009088).

Almost surely, 2^212005721 is an apocalyptic number.

It is an amenable number.

212005721 is a deficient number, since it is larger than the sum of its proper divisors (30631).

212005721 is a wasteful number, since it uses less digits than its factorization.

212005721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30630.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 212005721 is about 14560.4162371822. The cubic root of 212005721 is about 596.2785593723.

Adding to 212005721 its reverse (127500212), we get a palindrome (339505933).

The spelling of 212005721 in words is "two hundred twelve million, five thousand, seven hundred twenty-one".