21501228 has 96 divisors (see below), whose sum is σ = 61931520. Its totient is φ = 5670720.

The previous prime is 21501211. The next prime is 21501229. The reversal of 21501228 is 82210512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (21501229) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 59713 + ... + 60071.

It is an arithmetic number, because the mean of its divisors is an integer number (645120).

Almost surely, 2^21501228 is an apocalyptic number.

21501228 is a gapful number since it is divisible by the number (28) 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 21501228, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30965760).

21501228 is an abundant number, since it is smaller than the sum of its proper divisors (40430292).

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

21501228 is a wasteful number, since it uses less digits than its factorization.

21501228 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 427 (or 425 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 21501228 is about 4636.9416645026. The cubic root of 21501228 is about 278.0701822359.

The spelling of 21501228 in words is "twenty-one million, five hundred one thousand, two hundred twenty-eight".