21001280 has 28 divisors (see below), whose sum is σ = 50010060. Its totient is φ = 8400384.

The previous prime is 21001247. The next prime is 21001319. The reversal of 21001280 is 8210012.

It can be written as a sum of positive squares in 2 ways, for example, as 8667136 + 12334144 = 2944^2 + 3512^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32495 + ... + 33134.

Almost surely, 2^21001280 is an apocalyptic number.

21001280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001280 is an abundant number, since it is smaller than the sum of its proper divisors (29008780).

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

21001280 is an equidigital number, since it uses as much as digits as its factorization.

21001280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65646 (or 65636 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 21001280 is about 4582.7153522775. The cubic root of 21001280 is about 275.8980229575.

Adding to 21001280 its reverse (8210012), we get a palindrome (29211292).

The spelling of 21001280 in words is "twenty-one million, one thousand, two hundred eighty".