21019987 has 2 divisors, whose sum is σ = 21019988. Its totient is φ = 21019986.

The previous prime is 21019981. The next prime is 21019993. The reversal of 21019987 is 78991012.

It is a balanced prime because it is at equal distance from previous prime (21019981) and next prime (21019993).

It is a cyclic number.

It is not a de Polignac number, because 21019987 - 2³ = 21019979 is a prime.

It is not a weakly prime, because it can be changed into another prime (21019981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509993 + 10509994.

It is an arithmetic number, because the mean of its divisors is an integer number (10509994).

Almost surely, 2^21019987 is an apocalyptic number.

21019987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21019987 is an equidigital number, since it uses as much as digits as its factorization.

21019987 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21019987 is about 4584.7559367975. The cubic root of 21019987 is about 275.9799178485.

The spelling of 21019987 in words is "twenty-one million, nineteen thousand, nine hundred eighty-seven".