21216745 has 12 divisors (see below), whose sum is σ = 27985860. Its totient is φ = 15429920.

The previous prime is 21216743. The next prime is 21216751. The reversal of 21216745 is 54761212.

It can be written as a sum of positive squares in 2 ways, for example, as 16032016 + 5184729 = 4004^2 + 2277^2 .

It is not a de Polignac number, because 21216745 - 2¹ = 21216743 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21216743) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 16930 + ... + 18139.

It is an arithmetic number, because the mean of its divisors is an integer number (2332155).

Almost surely, 2^21216745 is an apocalyptic number.

It is an amenable number.

21216745 is a deficient number, since it is larger than the sum of its proper divisors (6769115).

21216745 is a wasteful number, since it uses less digits than its factorization.

21216745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35096 (or 35085 counting only the distinct ones).

The product of its digits is 3360, while the sum is 28.

The square root of 21216745 is about 4606.1638051637. The cubic root of 21216745 is about 276.8383500789.

Adding to 21216745 its reverse (54761212), we get a palindrome (75977957).

It can be divided in two parts, 212167 and 45, that added together give a palindrome (212212).

The spelling of 21216745 in words is "twenty-one million, two hundred sixteen thousand, seven hundred forty-five".