21617929 has 4 divisors (see below), whose sum is σ = 21669700. Its totient is φ = 21566160.

The previous prime is 21617927. The next prime is 21617969. The reversal of 21617929 is 92971612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 705600 + 20912329 = 840^2 + 4573^2 .

It is a cyclic number.

It is not a de Polignac number, because 21617929 - 2¹ = 21617927 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21617927) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 25254 + ... + 26095.

It is an arithmetic number, because the mean of its divisors is an integer number (5417425).

Almost surely, 2^21617929 is an apocalyptic number.

It is an amenable number.

21617929 is a deficient number, since it is larger than the sum of its proper divisors (51771).

21617929 is an equidigital number, since it uses as much as digits as its factorization.

21617929 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51770.

The product of its digits is 13608, while the sum is 37.

The square root of 21617929 is about 4649.5084686448. The cubic root of 21617929 is about 278.5723633793.

It can be divided in two parts, 216 and 17929, that added together give a triangular number (18145 = T₁₉₀).

The spelling of 21617929 in words is "twenty-one million, six hundred seventeen thousand, nine hundred twenty-nine".