21890987 has 2 divisors, whose sum is σ = 21890988. Its totient is φ = 21890986.

The previous prime is 21890959. The next prime is 21890993. The reversal of 21890987 is 78909812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21890987 - 2¹⁰ = 21889963 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21890927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10945493 + 10945494.

It is an arithmetic number, because the mean of its divisors is an integer number (10945494).

Almost surely, 2^21890987 is an apocalyptic number.

21890987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21890987 is an equidigital number, since it uses as much as digits as its factorization.

21890987 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72576, while the sum is 44.

The square root of 21890987 is about 4678.7805035073. The cubic root of 21890987 is about 279.7403502823.

The spelling of 21890987 in words is "twenty-one million, eight hundred ninety thousand, nine hundred eighty-seven".