21205061 has 4 divisors (see below), whose sum is σ = 21936300. Its totient is φ = 20473824.

The previous prime is 21205049. The next prime is 21205099. The reversal of 21205061 is 16050212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17181025 + 4024036 = 4145^2 + 2006^2 .

It is a cyclic number.

It is not a de Polignac number, because 21205061 - 2¹⁰ = 21204037 is a prime.

It is a super-2 number, since 2×21205061² = 899309224027442, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205021) 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, 365576 + ... + 365633.

It is an arithmetic number, because the mean of its divisors is an integer number (5484075).

Almost surely, 2^21205061 is an apocalyptic number.

It is an amenable number.

21205061 is a deficient number, since it is larger than the sum of its proper divisors (731239).

21205061 is an equidigital number, since it uses as much as digits as its factorization.

21205061 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 731238.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 21205061 is about 4604.8953299722. The cubic root of 21205061 is about 276.7875227218.

Adding to 21205061 its reverse (16050212), we get a palindrome (37255273).

The spelling of 21205061 in words is "twenty-one million, two hundred five thousand, sixty-one".