21891787 has 2 divisors, whose sum is σ = 21891788. Its totient is φ = 21891786.

The previous prime is 21891761. The next prime is 21891811. The reversal of 21891787 is 78719812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21891787 - 2²³ = 13503179 is a prime.

It is not a weakly prime, because it can be changed into another prime (21891757) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10945893 + 10945894.

It is an arithmetic number, because the mean of its divisors is an integer number (10945894).

Almost surely, 2^21891787 is an apocalyptic number.

21891787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21891787 is an equidigital number, since it uses as much as digits as its factorization.

21891787 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56448, while the sum is 43.

The square root of 21891787 is about 4678.8659950890. The cubic root of 21891787 is about 279.7437579185.

The spelling of 21891787 in words is "twenty-one million, eight hundred ninety-one thousand, seven hundred eighty-seven".