21115717 has 12 divisors (see below), whose sum is σ = 26009100. Its totient is φ = 17033856.

The previous prime is 21115657. The next prime is 21115723. The reversal of 21115717 is 71751112.

It can be written as a sum of positive squares in 2 ways, for example, as 12348196 + 8767521 = 3514^2 + 2961^2 .

It is not a de Polignac number, because 21115717 - 2¹⁵ = 21082949 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21115691 and 21115700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21115727) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11842 + ... + 13507.

It is an arithmetic number, because the mean of its divisors is an integer number (2167425).

Almost surely, 2^21115717 is an apocalyptic number.

It is an amenable number.

21115717 is a deficient number, since it is larger than the sum of its proper divisors (4893383).

21115717 is a wasteful number, since it uses less digits than its factorization.

21115717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25380 (or 25373 counting only the distinct ones).

The product of its digits is 490, while the sum is 25.

The square root of 21115717 is about 4595.1841094781. The cubic root of 21115717 is about 276.3982427461.

Adding to 21115717 its reverse (71751112), we get a palindrome (92866829).

The spelling of 21115717 in words is "twenty-one million, one hundred fifteen thousand, seven hundred seventeen".