21005545 has 16 divisors (see below), whose sum is σ = 28946880. Its totient is φ = 14472000.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005545 is 54550012.

It is not a de Polignac number, because 21005545 - 2¹⁷ = 20874473 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9006 + ... + 11095.

It is an arithmetic number, because the mean of its divisors is an integer number (1809180).

Almost surely, 2^21005545 is an apocalyptic number.

It is an amenable number.

21005545 is a deficient number, since it is larger than the sum of its proper divisors (7941335).

21005545 is a wasteful number, since it uses less digits than its factorization.

21005545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20136.

The product of its (nonzero) digits is 1000, while the sum is 22.

The square root of 21005545 is about 4583.1806641240. The cubic root of 21005545 is about 275.9166984131.

Adding to 21005545 its reverse (54550012), we get a palindrome (75555557).

The spelling of 21005545 in words is "twenty-one million, five thousand, five hundred forty-five".