21391048 has 48 divisors (see below), whose sum is σ = 47062620. Its totient is φ = 9088128.

The previous prime is 21391033. The next prime is 21391057. The reversal of 21391048 is 84019312.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20958084 + 432964 = 4578^2 + 658^2 .

It is a Harshad number since it is a multiple of its sum of digits (28).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 77086 + ... + 77362.

Almost surely, 2^21391048 is an apocalyptic number.

21391048 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21391048, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23531310).

21391048 is an abundant number, since it is smaller than the sum of its proper divisors (25671572).

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

21391048 is a wasteful number, since it uses less digits than its factorization.

21391048 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 494 (or 483 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21391048 is about 4625.0457295037. The cubic root of 21391048 is about 277.5943915019.

The spelling of 21391048 in words is "twenty-one million, three hundred ninety-one thousand, forty-eight".