21081220 has 12 divisors (see below), whose sum is σ = 44270604. Its totient is φ = 8432480.

The previous prime is 21081217. The next prime is 21081259. The reversal of 21081220 is 2218012.

It can be written as a sum of positive squares in 2 ways, for example, as 13060996 + 8020224 = 3614^2 + 2832^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21081194 and 21081203.

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, 527011 + ... + 527050.

It is an arithmetic number, because the mean of its divisors is an integer number (3689217).

Almost surely, 2^21081220 is an apocalyptic number.

21081220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21081220 is an abundant number, since it is smaller than the sum of its proper divisors (23189384).

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

21081220 is a wasteful number, since it uses less digits than its factorization.

21081220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1054070 (or 1054068 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 16.

The square root of 21081220 is about 4591.4289714641. The cubic root of 21081220 is about 276.2476423295.

Adding to 21081220 its reverse (2218012), we get a palindrome (23299232).

The spelling of 21081220 in words is "twenty-one million, eighty-one thousand, two hundred twenty".