21447729 has 6 divisors (see below), whose sum is σ = 30980066. Its totient is φ = 14298480.

The previous prime is 21447719. The next prime is 21447743. The reversal of 21447729 is 92774412.

It can be written as a sum of positive squares in only one way, i.e., 20007729 + 1440000 = 4473^2 + 1200^2 .

It is not a de Polignac number, because 21447729 - 2⁵ = 21447697 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21447693 and 21447702.

It is not an unprimeable number, because it can be changed into a prime (21447709) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1191532 + ... + 1191549.

Almost surely, 2^21447729 is an apocalyptic number.

It is an amenable number.

21447729 is a deficient number, since it is larger than the sum of its proper divisors (9532337).

21447729 is a wasteful number, since it uses less digits than its factorization.

21447729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2383087 (or 2383084 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21447729 is about 4631.1692907947. The cubic root of 21447729 is about 277.8393608113.

The spelling of 21447729 in words is "twenty-one million, four hundred forty-seven thousand, seven hundred twenty-nine".