21001205 has 8 divisors (see below), whose sum is σ = 26683992. Its totient is φ = 15812608.

The previous prime is 21001187. The next prime is 21001247. The reversal of 21001205 is 50210012.

It can be written as a sum of positive squares in 4 ways, for example, as 11771761 + 9229444 = 3431^2 + 3038^2 .

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 21001205 - 2²² = 16806901 is a prime.

It is a super-2 number, since 2×21001205² = 882101222904050, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 123452 + ... + 123621.

It is an arithmetic number, because the mean of its divisors is an integer number (3335499).

Almost surely, 2^21001205 is an apocalyptic number.

It is an amenable number.

21001205 is a deficient number, since it is larger than the sum of its proper divisors (5682787).

21001205 is a wasteful number, since it uses less digits than its factorization.

21001205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 247095.

The product of its (nonzero) digits is 20, while the sum is 11.

The square root of 21001205 is about 4582.7071693487. The cubic root of 21001205 is about 275.8976945271.

Adding to 21001205 its reverse (50210012), we get a palindrome (71211217).

The spelling of 21001205 in words is "twenty-one million, one thousand, two hundred five".