20721225 has 48 divisors (see below), whose sum is σ = 40533120. Its totient is φ = 9139200.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721225 is 52212702.

It is a happy number.

It is not a de Polignac number, because 20721225 - 2¹ = 20721223 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20721223) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 14545 + ... + 15905.

It is an arithmetic number, because the mean of its divisors is an integer number (844440).

Almost surely, 2^20721225 is an apocalyptic number.

20721225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

20721225 is a deficient number, since it is larger than the sum of its proper divisors (19811895).

20721225 is a wasteful number, since it uses less digits than its factorization.

20721225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1410 (or 1405 counting only the distinct ones).

The product of its (nonzero) digits is 560, while the sum is 21.

The square root of 20721225 is about 4552.0572272325. The cubic root of 20721225 is about 274.6661513472. Note that the first 3 decimals are identical.

Adding to 20721225 its reverse (52212702), we get a palindrome (72933927).

The spelling of 20721225 in words is "twenty million, seven hundred twenty-one thousand, two hundred twenty-five".