21151220 has 12 divisors (see below), whose sum is σ = 44417604. Its totient is φ = 8460480.

The previous prime is 21151219. The next prime is 21151241. The reversal of 21151220 is 2215112.

It can be written as a sum of positive squares in 2 ways, for example, as 14577124 + 6574096 = 3818^2 + 2564^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21151195 and 21151204.

It is a congruent number.

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, 528761 + ... + 528800.

It is an arithmetic number, because the mean of its divisors is an integer number (3701467).

Almost surely, 2^21151220 is an apocalyptic number.

21151220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21151220 is an abundant number, since it is smaller than the sum of its proper divisors (23266384).

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

21151220 is a wasteful number, since it uses less digits than its factorization.

21151220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1057570 (or 1057568 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 21151220 is about 4599.0455531556. The cubic root of 21151220 is about 276.5530637933.

Adding to 21151220 its reverse (2215112), we get a palindrome (23366332).

The spelling of 21151220 in words is "twenty-one million, one hundred fifty-one thousand, two hundred twenty".