21005761 has 24 divisors (see below), whose sum is σ = 26199936. Its totient is φ = 16732800.

The previous prime is 21005759. The next prime is 21005767. The reversal of 21005761 is 16750012.

It is not a de Polignac number, because 21005761 - 2¹ = 21005759 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005767) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 125700 + ... + 125866.

It is an arithmetic number, because the mean of its divisors is an integer number (1091664).

Almost surely, 2^21005761 is an apocalyptic number.

It is an amenable number.

21005761 is a deficient number, since it is larger than the sum of its proper divisors (5194175).

21005761 is a wasteful number, since it uses less digits than its factorization.

21005761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 349 (or 342 counting only the distinct ones).

The product of its (nonzero) digits is 420, while the sum is 22.

The square root of 21005761 is about 4583.2042284847. The cubic root of 21005761 is about 275.9176441603.

Adding to 21005761 its reverse (16750012), we get a palindrome (37755773).

The spelling of 21005761 in words is "twenty-one million, five thousand, seven hundred sixty-one".