21154640 has 40 divisors (see below), whose sum is σ = 52970568. Its totient is φ = 7810560.

The previous prime is 21154631. The next prime is 21154669. The reversal of 21154640 is 4645112.

It can be written as a sum of positive squares in 4 ways, for example, as 760384 + 20394256 = 872^2 + 4516^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9131 + ... + 11210.

Almost surely, 2^21154640 is an apocalyptic number.

21154640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21154640 is an abundant number, since it is smaller than the sum of its proper divisors (31815928).

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

21154640 is a wasteful number, since it uses less digits than its factorization.

21154640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20367 (or 20361 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 23.

The square root of 21154640 is about 4599.4173544048. The cubic root of 21154640 is about 276.5679685365.

Adding to 21154640 its reverse (4645112), we get a palindrome (25799752).

The spelling of 21154640 in words is "twenty-one million, one hundred fifty-four thousand, six hundred forty".