21572281 has 4 divisors (see below), whose sum is σ = 21832272. Its totient is φ = 21312292.

The previous prime is 21572279. The next prime is 21572297. The reversal of 21572281 is 18227512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21572281 - 2¹ = 21572279 is a prime.

It is a super-2 number, since 2×21572281² = 930726615085922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21572231) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 129871 + ... + 130036.

It is an arithmetic number, because the mean of its divisors is an integer number (5458068).

Almost surely, 2^21572281 is an apocalyptic number.

It is an amenable number.

21572281 is a deficient number, since it is larger than the sum of its proper divisors (259991).

21572281 is an equidigital number, since it uses as much as digits as its factorization.

21572281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 259990.

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

The square root of 21572281 is about 4644.5969685216. The cubic root of 21572281 is about 278.3761492055.

Adding to 21572281 its reverse (18227512), we get a palindrome (39799793).

The spelling of 21572281 in words is "twenty-one million, five hundred seventy-two thousand, two hundred eighty-one".