21790205 has 8 divisors (see below), whose sum is σ = 26244312. Its totient is φ = 17368128.

The previous prime is 21790201. The next prime is 21790213. The reversal of 21790205 is 50209712.

It can be written as a sum of positive squares in 4 ways, for example, as 158404 + 21631801 = 398^2 + 4651^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21790205 - 2² = 21790201 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21790201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6482 + ... + 9251.

It is an arithmetic number, because the mean of its divisors is an integer number (3280539).

Almost surely, 2^21790205 is an apocalyptic number.

It is an amenable number.

21790205 is a deficient number, since it is larger than the sum of its proper divisors (4454107).

21790205 is a wasteful number, since it uses less digits than its factorization.

21790205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16015.

The product of its (nonzero) digits is 1260, while the sum is 26.

The square root of 21790205 is about 4667.9979648667. The cubic root of 21790205 is about 279.3103990920.

Adding to 21790205 its reverse (50209712), we get a palindrome (71999917).

The spelling of 21790205 in words is "twenty-one million, seven hundred ninety thousand, two hundred five".