21243515 has 16 divisors (see below), whose sum is σ = 26524800. Its totient is φ = 16313472.

The previous prime is 21243503. The next prime is 21243517. The reversal of 21243515 is 51534212.

It is a cyclic number.

It is not a de Polignac number, because 21243515 - 2⁸ = 21243259 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21243517) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 34349 + ... + 34961.

It is an arithmetic number, because the mean of its divisors is an integer number (1657800).

Almost surely, 2^21243515 is an apocalyptic number.

21243515 is a deficient number, since it is larger than the sum of its proper divisors (5281285).

21243515 is a wasteful number, since it uses less digits than its factorization.

21243515 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 886.

The product of its digits is 1200, while the sum is 23.

The square root of 21243515 is about 4609.0687779637. The cubic root of 21243515 is about 276.9547337484.

Adding to 21243515 its reverse (51534212), we get a palindrome (72777727).

The spelling of 21243515 in words is "twenty-one million, two hundred forty-three thousand, five hundred fifteen".