21451240 has 16 divisors (see below), whose sum is σ = 48265380. Its totient is φ = 8580480.

The previous prime is 21451237. The next prime is 21451277. The reversal of 21451240 is 4215412.

It can be written as a sum of positive squares in 2 ways, for example, as 21325924 + 125316 = 4618^2 + 354^2 .

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, 268101 + ... + 268180.

Almost surely, 2^21451240 is an apocalyptic number.

21451240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21451240 is an abundant number, since it is smaller than the sum of its proper divisors (26814140).

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

21451240 is a wasteful number, since it uses less digits than its factorization.

21451240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 536292 (or 536288 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21451240 is about 4631.5483372194. The cubic root of 21451240 is about 277.8545207811.

Adding to 21451240 its reverse (4215412), we get a palindrome (25666652).

The spelling of 21451240 in words is "twenty-one million, four hundred fifty-one thousand, two hundred forty".