21681545 has 8 divisors (see below), whose sum is σ = 27548424. Its totient is φ = 16324864.

The previous prime is 21681533. The next prime is 21681547. The reversal of 21681545 is 54518612.

It can be written as a sum of positive squares in 4 ways, for example, as 5968249 + 15713296 = 2443^2 + 3964^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21681545 - 2⁴ = 21681529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21681547) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 127454 + ... + 127623.

It is an arithmetic number, because the mean of its divisors is an integer number (3443553).

Almost surely, 2^21681545 is an apocalyptic number.

It is an amenable number.

21681545 is a deficient number, since it is larger than the sum of its proper divisors (5866879).

21681545 is a wasteful number, since it uses less digits than its factorization.

21681545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 255099.

The product of its digits is 9600, while the sum is 32.

The square root of 21681545 is about 4656.3445963545. The cubic root of 21681545 is about 278.8453513608.

The spelling of 21681545 in words is "twenty-one million, six hundred eighty-one thousand, five hundred forty-five".