21461781 has 32 divisors (see below), whose sum is σ = 32394240. Its totient is φ = 12528000.

The previous prime is 21461779. The next prime is 21461789. The reversal of 21461781 is 18716412.

It is not a de Polignac number, because 21461781 - 2¹ = 21461779 is a prime.

It is a super-2 number, since 2×21461781² = 921216087383922, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21461789) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 142056 + ... + 142206.

It is an arithmetic number, because the mean of its divisors is an integer number (1012320).

Almost surely, 2^21461781 is an apocalyptic number.

It is an amenable number.

21461781 is a deficient number, since it is larger than the sum of its proper divisors (10932459).

21461781 is a wasteful number, since it uses less digits than its factorization.

21461781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 297.

The product of its digits is 2688, while the sum is 30.

The square root of 21461781 is about 4632.6861538421. The cubic root of 21461781 is about 277.9000252973.

The spelling of 21461781 in words is "twenty-one million, four hundred sixty-one thousand, seven hundred eighty-one".