21115278 has 48 divisors (see below), whose sum is σ = 47923200. Its totient is φ = 6711120.

The previous prime is 21115261. The next prime is 21115307. The reversal of 21115278 is 87251112.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 43843 + ... + 44321.

It is an arithmetic number, because the mean of its divisors is an integer number (998400).

Almost surely, 2^21115278 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21115278, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23961600).

21115278 is an abundant number, since it is smaller than the sum of its proper divisors (26807922).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21115278 is a wasteful number, since it uses less digits than its factorization.

21115278 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 597 (or 594 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21115278 is about 4595.1363418293. The cubic root of 21115278 is about 276.3963272745.

Subtracting from 21115278 its sum of digits (27), we obtain a triangular number (21115251 = T₆₄₉₈).

The spelling of 21115278 in words is "twenty-one million, one hundred fifteen thousand, two hundred seventy-eight".