21553317 has 8 divisors (see below), whose sum is σ = 31930880. Its totient is φ = 14368860.

The previous prime is 21553309. The next prime is 21553319. The reversal of 21553317 is 71335512.

It is not a de Polignac number, because 21553317 - 2³ = 21553309 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 798271 = 21553317 / (2 + 1 + 5 + 5 + 3 + 3 + 1 + 7).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21553319) 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, 399109 + ... + 399162.

It is an arithmetic number, because the mean of its divisors is an integer number (3991360).

Almost surely, 2^21553317 is an apocalyptic number.

21553317 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21553317 is a deficient number, since it is larger than the sum of its proper divisors (10377563).

21553317 is an equidigital number, since it uses as much as digits as its factorization.

21553317 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 798280 (or 798274 counting only the distinct ones).

The product of its digits is 3150, while the sum is 27.

The square root of 21553317 is about 4642.5550077517. Note that the first 3 decimals coincide. The cubic root of 21553317 is about 278.2945526265.

Adding to 21553317 its reverse (71335512), we get a palindrome (92888829).

The spelling of 21553317 in words is "twenty-one million, five hundred fifty-three thousand, three hundred seventeen".