21787915987 has 2 divisors, whose sum is σ = 21787915988. Its totient is φ = 21787915986.

The previous prime is 21787915973. The next prime is 21787915991. The reversal of 21787915987 is 78951978712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21787915987 - 2⁷ = 21787915859 is a prime.

It is not a weakly prime, because it can be changed into another prime (21787915927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893957993 + 10893957994.

It is an arithmetic number, because the mean of its divisors is an integer number (10893957994).

Almost surely, 2^21787915987 is an apocalyptic number.

21787915987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21787915987 is an equidigital number, since it uses as much as digits as its factorization.

21787915987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 17781120, while the sum is 64.

The spelling of 21787915987 in words is "twenty-one billion, seven hundred eighty-seven million, nine hundred fifteen thousand, nine hundred eighty-seven".