21638719 has 2 divisors, whose sum is σ = 21638720. Its totient is φ = 21638718.

The previous prime is 21638689. The next prime is 21638723. The reversal of 21638719 is 91783612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21638719 - 2¹³ = 21630527 is a prime.

It is a super-2 number, since 2×21638719² = 936468319921922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21638759) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10819359 + 10819360.

It is an arithmetic number, because the mean of its divisors is an integer number (10819360).

Almost surely, 2^21638719 is an apocalyptic number.

21638719 is a deficient number, since it is larger than the sum of its proper divisors (1).

21638719 is an equidigital number, since it uses as much as digits as its factorization.

21638719 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 37.

The square root of 21638719 is about 4651.7436515784. The cubic root of 21638719 is about 278.6616359434.

The spelling of 21638719 in words is "twenty-one million, six hundred thirty-eight thousand, seven hundred nineteen".