21287951 has 2 divisors, whose sum is σ = 21287952. Its totient is φ = 21287950.

The previous prime is 21287921. The next prime is 21287993. The reversal of 21287951 is 15978212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21287951 - 2¹⁴ = 21271567 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21287921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10643975 + 10643976.

It is an arithmetic number, because the mean of its divisors is an integer number (10643976).

Almost surely, 2^21287951 is an apocalyptic number.

21287951 is a deficient number, since it is larger than the sum of its proper divisors (1).

21287951 is an equidigital number, since it uses as much as digits as its factorization.

21287951 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10080, while the sum is 35.

The square root of 21287951 is about 4613.8867563043. The cubic root of 21287951 is about 277.1477054175.

The spelling of 21287951 in words is "twenty-one million, two hundred eighty-seven thousand, nine hundred fifty-one".