21287461 has 4 divisors (see below), whose sum is σ = 22924972. Its totient is φ = 19649952.

The previous prime is 21287459. The next prime is 21287531. The reversal of 21287461 is 16478212.

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 6155361 + 15132100 = 2481^2 + 3890^2 .

It is a cyclic number.

It is not a de Polignac number, because 21287461 - 2¹ = 21287459 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287411) 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, 818736 + ... + 818761.

It is an arithmetic number, because the mean of its divisors is an integer number (5731243).

Almost surely, 2^21287461 is an apocalyptic number.

It is an amenable number.

21287461 is a deficient number, since it is larger than the sum of its proper divisors (1637511).

21287461 is a wasteful number, since it uses less digits than its factorization.

21287461 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1637510.

The product of its digits is 5376, while the sum is 31.

The square root of 21287461 is about 4613.8336554323. The cubic root of 21287461 is about 277.1455789655.

Subtracting from 21287461 its reverse (16478212), we obtain a square (4809249 = 2193²).

The spelling of 21287461 in words is "twenty-one million, two hundred eighty-seven thousand, four hundred sixty-one".