21005220 has 24 divisors (see below), whose sum is σ = 58814784. Its totient is φ = 5601376.

The previous prime is 21005219. The next prime is 21005227. The reversal of 21005220 is 2250012.

It is a super-3 number, since 3×21005220³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a junction number, because it is equal to n+sod(n) for n = 21005196 and 21005205.

It is not an unprimeable number, because it can be changed into a prime (21005227) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 174984 + ... + 175103.

It is an arithmetic number, because the mean of its divisors is an integer number (2450616).

Almost surely, 2^21005220 is an apocalyptic number.

21005220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005220 is an abundant number, since it is smaller than the sum of its proper divisors (37809564).

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

21005220 is a wasteful number, since it uses less digits than its factorization.

21005220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 350099 (or 350097 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 12.

The square root of 21005220 is about 4583.1452082604. The cubic root of 21005220 is about 275.9152754017.

Adding to 21005220 its reverse (2250012), we get a palindrome (23255232).

The spelling of 21005220 in words is "twenty-one million, five thousand, two hundred twenty".