21287617 has 8 divisors (see below), whose sum is σ = 23545256. Its totient is φ = 19118592.

The previous prime is 21287551. The next prime is 21287633. The reversal of 21287617 is 71678212.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 8904256 + 12383361 = 2984^2 + 3519^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21287617 - 2¹¹ = 21285569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21237617) 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, 21648 + ... + 22609.

It is an arithmetic number, because the mean of its divisors is an integer number (2943157).

Almost surely, 2^21287617 is an apocalyptic number.

It is an amenable number.

21287617 is a deficient number, since it is larger than the sum of its proper divisors (2257639).

21287617 is a wasteful number, since it uses less digits than its factorization.

21287617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44307.

The product of its digits is 9408, while the sum is 34.

The square root of 21287617 is about 4613.8505610824. The cubic root of 21287617 is about 277.1462559619.

It can be divided in two parts, 21287 and 617, that added together give a square (21904 = 148²).

The spelling of 21287617 in words is "twenty-one million, two hundred eighty-seven thousand, six hundred seventeen".