21501287 has 2 divisors, whose sum is σ = 21501288. Its totient is φ = 21501286.

The previous prime is 21501281. The next prime is 21501289. The reversal of 21501287 is 78210512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21501287 - 2⁸ = 21501031 is a prime.

Together with 21501289, it forms a pair of twin primes.

It is a Chen prime.

It is a zygodrome in base 9.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21501281) 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, 10750643 + 10750644.

It is an arithmetic number, because the mean of its divisors is an integer number (10750644).

Almost surely, 2^21501287 is an apocalyptic number.

21501287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21501287 is an equidigital number, since it uses as much as digits as its factorization.

21501287 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21501287 is about 4636.9480264502. The cubic root of 21501287 is about 278.0704365799.

Adding to 21501287 its reverse (78210512), we get a palindrome (99711799).

The spelling of 21501287 in words is "twenty-one million, five hundred one thousand, two hundred eighty-seven".