21611620 has 24 divisors (see below), whose sum is σ = 45521784. Its totient is φ = 8618496.

The previous prime is 21611617. The next prime is 21611621. The reversal of 21611620 is 2611612.

It can be written as a sum of positive squares in 4 ways, for example, as 322624 + 21288996 = 568^2 + 4614^2 .

It is not an unprimeable number, because it can be changed into a prime (21611621) 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, 6012 + ... + 8908.

It is an arithmetic number, because the mean of its divisors is an integer number (1896741).

Almost surely, 2^21611620 is an apocalyptic number.

21611620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21611620 is an abundant number, since it is smaller than the sum of its proper divisors (23910164).

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

21611620 is a wasteful number, since it uses less digits than its factorization.

21611620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3279 (or 3277 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21611620 is about 4648.8299603234. The cubic root of 21611620 is about 278.5452611218.

It can be divided in two parts, 216 and 11620, that multiplied together give a triangular number (2509920 = T₂₂₄₀).

The spelling of 21611620 in words is "twenty-one million, six hundred eleven thousand, six hundred twenty".