21508787 has 2 divisors, whose sum is σ = 21508788. Its totient is φ = 21508786.

The previous prime is 21508771. The next prime is 21508789. The reversal of 21508787 is 78780512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21508787 - 2⁴ = 21508771 is a prime.

It is a super-2 number, since 2×21508787² = 925255836422738, which contains 22 as substring.

Together with 21508789, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21508787.

It is not a weakly prime, because it can be changed into another prime (21508789) 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, 10754393 + 10754394.

It is an arithmetic number, because the mean of its divisors is an integer number (10754394).

Almost surely, 2^21508787 is an apocalyptic number.

21508787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21508787 is an equidigital number, since it uses as much as digits as its factorization.

21508787 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 31360, while the sum is 38.

The square root of 21508787 is about 4637.7566775328. The cubic root of 21508787 is about 278.1027646576.

The spelling of 21508787 in words is "twenty-one million, five hundred eight thousand, seven hundred eighty-seven".