21288415 has 16 divisors (see below), whose sum is σ = 26301312. Its totient is φ = 16533504.

The previous prime is 21288359. The next prime is 21288419. The reversal of 21288415 is 51488212.

It is a cyclic number.

It is not a de Polignac number, because 21288415 - 2¹³ = 21280223 is a prime.

It is a super-2 number, since 2×21288415² = 906393226424450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21288419) 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, 36607 + ... + 37183.

It is an arithmetic number, because the mean of its divisors is an integer number (1643832).

Almost surely, 2^21288415 is an apocalyptic number.

21288415 is a deficient number, since it is larger than the sum of its proper divisors (5012897).

21288415 is a wasteful number, since it uses less digits than its factorization.

21288415 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 786.

The product of its digits is 5120, while the sum is 31.

The square root of 21288415 is about 4613.9370390156. The cubic root of 21288415 is about 277.1497190073.

It can be divided in two parts, 2128 and 8415, that multiplied together give a triangular number (17907120 = T₅₉₈₄).

The spelling of 21288415 in words is "twenty-one million, two hundred eighty-eight thousand, four hundred fifteen".