21217938769 has 4 divisors (see below), whose sum is σ = 21949591860. Its totient is φ = 20486285680.

The previous prime is 21217938757. The next prime is 21217938787. The reversal of 21217938769 is 96783971212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13986137169 + 7231801600 = 118263^2 + 85040^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217938769 - 2¹⁷ = 21217807697 is a prime.

It is a super-2 number, since 2×21217938769² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21217938719) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 365826502 + ... + 365826559.

It is an arithmetic number, because the mean of its divisors is an integer number (5487397965).

Almost surely, 2^21217938769 is an apocalyptic number.

21217938769 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21217938769 is a deficient number, since it is larger than the sum of its proper divisors (731653091).

21217938769 is an equidigital number, since it uses as much as digits as its factorization.

21217938769 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 731653090.

The product of its digits is 2286144, while the sum is 55.

The spelling of 21217938769 in words is "twenty-one billion, two hundred seventeen million, nine hundred thirty-eight thousand, seven hundred sixty-nine".