21779987 has 2 divisors, whose sum is σ = 21779988. Its totient is φ = 21779986.

The previous prime is 21779981. The next prime is 21780001. The reversal of 21779987 is 78997712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21779987 - 2⁴ = 21779971 is a prime.

It is not a weakly prime, because it can be changed into another prime (21779981) 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, 10889993 + 10889994.

It is an arithmetic number, because the mean of its divisors is an integer number (10889994).

Almost surely, 2^21779987 is an apocalyptic number.

21779987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21779987 is an equidigital number, since it uses as much as digits as its factorization.

21779987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 444528, while the sum is 50.

The square root of 21779987 is about 4666.9033630449. The cubic root of 21779987 is about 279.2667336029.

The spelling of 21779987 in words is "twenty-one million, seven hundred seventy-nine thousand, nine hundred eighty-seven".