21805461 has 6 divisors (see below), whose sum is σ = 31496790. Its totient is φ = 14536968.

The previous prime is 21805451. The next prime is 21805463. The reversal of 21805461 is 16450812.

It can be written as a sum of positive squares in only one way, i.e., 14676561 + 7128900 = 3831^2 + 2670^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21805461 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805463) by changing a digit.

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 5 ways as a sum of consecutive naturals, for example, 1211406 + ... + 1211423.

It is an arithmetic number, because the mean of its divisors is an integer number (5249465).

Almost surely, 2^21805461 is an apocalyptic number.

It is an amenable number.

21805461 is a deficient number, since it is larger than the sum of its proper divisors (9691329).

21805461 is a wasteful number, since it uses less digits than its factorization.

21805461 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2422835 (or 2422832 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21805461 is about 4669.6317841988. The cubic root of 21805461 is about 279.3755685168.

The spelling of 21805461 in words is "twenty-one million, eight hundred five thousand, four hundred sixty-one".