21185280 has 144 divisors (see below), whose sum is σ = 75300960. Its totient is φ = 5640192.

The previous prime is 21185261. The next prime is 21185287. The reversal of 21185280 is 8258112.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21185287) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 34254 + ... + 34866.

Almost surely, 2^21185280 is an apocalyptic number.

21185280 is a gapful number since it is divisible by the number (20) 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 21185280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37650480).

21185280 is an abundant number, since it is smaller than the sum of its proper divisors (54115680).

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

21185280 is an equidigital number, since it uses as much as digits as its factorization.

21185280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 643 (or 623 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 21185280 is about 4602.7470058651. The cubic root of 21185280 is about 276.7014294798.

It can be divided in two parts, 211 and 85280, that added together give a triangular number (85491 = T₄₁₃).

The spelling of 21185280 in words is "twenty-one million, one hundred eighty-five thousand, two hundred eighty".