21151620 has 72 divisors (see below), whose sum is σ = 73329984. Its totient is φ = 4834368.

The previous prime is 21151619. The next prime is 21151639. The reversal of 21151620 is 2615112.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21151593 and 21151602.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7134 + ... + 9653.

It is an arithmetic number, because the mean of its divisors is an integer number (1018472).

Almost surely, 2^21151620 is an apocalyptic number.

21151620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21151620 is an abundant number, since it is smaller than the sum of its proper divisors (52178364).

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

21151620 is a wasteful number, since it uses less digits than its factorization.

21151620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16809 (or 16804 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 21151620 is about 4599.0890402339. The cubic root of 21151620 is about 276.5548071211.

Adding to 21151620 its reverse (2615112), we get a palindrome (23766732).

The spelling of 21151620 in words is "twenty-one million, one hundred fifty-one thousand, six hundred twenty".