21505040 has 20 divisors (see below), whose sum is σ = 49999404. Its totient is φ = 8601984.

The previous prime is 21505039. The next prime is 21505063. The reversal of 21505040 is 4050512.

It can be written as a sum of positive squares in 2 ways, for example, as 7246864 + 14258176 = 2692^2 + 3776^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134327 + ... + 134486.

Almost surely, 2^21505040 is an apocalyptic number.

21505040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21505040 is an abundant number, since it is smaller than the sum of its proper divisors (28494364).

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

21505040 is a wasteful number, since it uses less digits than its factorization.

21505040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268826 (or 268820 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 17.

The square root of 21505040 is about 4637.3526930782. The cubic root of 21505040 is about 278.0866144895.

Adding to 21505040 its reverse (4050512), we get a palindrome (25555552).

The spelling of 21505040 in words is "twenty-one million, five hundred five thousand, forty".