21217825 has 6 divisors (see below), whose sum is σ = 26310134. Its totient is φ = 16974240.

The previous prime is 21217747. The next prime is 21217829. The reversal of 21217825 is 52871212.

It can be written as a sum of positive squares in 3 ways, for example, as 1361889 + 19855936 = 1167^2 + 4456^2 .

It is not a de Polignac number, because 21217825 - 2⁷ = 21217697 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21217793 and 21217802.

It is not an unprimeable number, because it can be changed into a prime (21217829) 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, 424332 + ... + 424381.

Almost surely, 2^21217825 is an apocalyptic number.

21217825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21217825 is a deficient number, since it is larger than the sum of its proper divisors (5092309).

21217825 is an equidigital number, since it uses as much as digits as its factorization.

21217825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 848723 (or 848718 counting only the distinct ones).

The product of its digits is 2240, while the sum is 28.

The square root of 21217825 is about 4606.2810378873. The cubic root of 21217825 is about 276.8430473176.

The spelling of 21217825 in words is "twenty-one million, two hundred seventeen thousand, eight hundred twenty-five".