21191281 has 4 divisors (see below), whose sum is σ = 21205492. Its totient is φ = 21177072.

The previous prime is 21191279. The next prime is 21191309. The reversal of 21191281 is 18219112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14861025 + 6330256 = 3855^2 + 2516^2 .

It is a cyclic number.

It is not a de Polignac number, because 21191281 - 2¹ = 21191279 is a prime.

It is a super-2 number, since 2×21191281² = 898140780841922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21191201) 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, 4566 + ... + 7951.

It is an arithmetic number, because the mean of its divisors is an integer number (5301373).

Almost surely, 2^21191281 is an apocalyptic number.

It is an amenable number.

21191281 is a deficient number, since it is larger than the sum of its proper divisors (14211).

21191281 is a wasteful number, since it uses less digits than its factorization.

21191281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14210.

The product of its digits is 288, while the sum is 25.

The square root of 21191281 is about 4603.3988530215. The cubic root of 21191281 is about 276.7275534130.

The spelling of 21191281 in words is "twenty-one million, one hundred ninety-one thousand, two hundred eighty-one".