21789997 has 2 divisors, whose sum is σ = 21789998. Its totient is φ = 21789996.

The previous prime is 21789967. The next prime is 21790001. The reversal of 21789997 is 79998712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20304036 + 1485961 = 4506^2 + 1219^2 .

It is a cyclic number.

It is not a de Polignac number, because 21789997 - 2¹¹ = 21787949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21789917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10894998 + 10894999.

It is an arithmetic number, because the mean of its divisors is an integer number (10894999).

Almost surely, 2^21789997 is an apocalyptic number.

It is an amenable number.

21789997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21789997 is an equidigital number, since it uses as much as digits as its factorization.

21789997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 571536, while the sum is 52.

The square root of 21789997 is about 4667.9756854551. The cubic root of 21789997 is about 279.3095103632.

The spelling of 21789997 in words is "twenty-one million, seven hundred eighty-nine thousand, nine hundred ninety-seven".