21021345 has 12 divisors (see below), whose sum is σ = 36437076. Its totient is φ = 11211360.

The previous prime is 21021331. The next prime is 21021349. The reversal of 21021345 is 54312012.

It can be written as a sum of positive squares in 2 ways, for example, as 13220496 + 7800849 = 3636^2 + 2793^2 .

It is not a de Polignac number, because 21021345 - 2¹⁸ = 20759201 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21021349) 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, 233526 + ... + 233615.

It is an arithmetic number, because the mean of its divisors is an integer number (3036423).

Almost surely, 2^21021345 is an apocalyptic number.

It is an amenable number.

21021345 is a deficient number, since it is larger than the sum of its proper divisors (15415731).

21021345 is a wasteful number, since it uses less digits than its factorization.

21021345 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 467152 (or 467149 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21021345 is about 4584.9040338921. The cubic root of 21021345 is about 275.9858609644.

Adding to 21021345 its reverse (54312012), we get a palindrome (75333357).

The spelling of 21021345 in words is "twenty-one million, twenty-one thousand, three hundred forty-five".