21005541 has 32 divisors (see below), whose sum is σ = 32592000. Its totient is φ = 13353984.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005541 is 14550012.

It is not a de Polignac number, because 21005541 - 2¹ = 21005539 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005561) 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, 108741 + ... + 108933.

It is an arithmetic number, because the mean of its divisors is an integer number (1018500).

Almost surely, 2^21005541 is an apocalyptic number.

It is an amenable number.

21005541 is a deficient number, since it is larger than the sum of its proper divisors (11586459).

21005541 is a wasteful number, since it uses less digits than its factorization.

21005541 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 370 (or 364 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21005541 is about 4583.1802277458. The cubic root of 21005541 is about 275.9166808992.

Adding to 21005541 its reverse (14550012), we get a palindrome (35555553).

The spelling of 21005541 in words is "twenty-one million, five thousand, five hundred forty-one".