21785620 has 24 divisors (see below), whose sum is σ = 45839304. Its totient is φ = 8697216.

The previous prime is 21785611. The next prime is 21785629. The reversal of 21785620 is 2658712.

It is an interprime number because it is at equal distance from previous prime (21785611) and next prime (21785629).

It can be written as a sum of positive squares in 4 ways, for example, as 367236 + 21418384 = 606^2 + 4628^2 .

It is a super-2 number, since 2×21785620² = 949226477568800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21785629) 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, 16422 + ... + 17698.

It is an arithmetic number, because the mean of its divisors is an integer number (1909971).

Almost surely, 2^21785620 is an apocalyptic number.

21785620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21785620 is an abundant number, since it is smaller than the sum of its proper divisors (24053684).

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

21785620 is a wasteful number, since it uses less digits than its factorization.

21785620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2139 (or 2137 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 21785620 is about 4667.5068291327. The cubic root of 21785620 is about 279.2908072920.

The spelling of 21785620 in words is "twenty-one million, seven hundred eighty-five thousand, six hundred twenty".