21751281 has 16 divisors (see below), whose sum is σ = 32529600. Its totient is φ = 14363424.

The previous prime is 21751237. The next prime is 21751283. The reversal of 21751281 is 18215712.

It is not a de Polignac number, because 21751281 - 2⁶ = 21751217 is a prime.

It is a super-2 number, since 2×21751281² = 946236450281922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21751283) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 876 + ... + 6653.

It is an arithmetic number, because the mean of its divisors is an integer number (2033100).

Almost surely, 2^21751281 is an apocalyptic number.

It is an amenable number.

21751281 is a deficient number, since it is larger than the sum of its proper divisors (10778319).

21751281 is a wasteful number, since it uses less digits than its factorization.

21751281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7645 (or 7639 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21751281 is about 4663.8268621380. The cubic root of 21751281 is about 279.1439885739.

Adding to 21751281 its reverse (18215712), we get a palindrome (39966993).

The spelling of 21751281 in words is "twenty-one million, seven hundred fifty-one thousand, two hundred eighty-one".