21870387217 has 6 divisors (see below), whose sum is σ = 25441062738. Its totient is φ = 18746046144.

The previous prime is 21870387199. The next prime is 21870387229. The reversal of 21870387217 is 71278307812.

It can be written as a sum of positive squares in only one way, i.e., 21831835536 + 38551681 = 147756^2 + 6209^2 .

It is not a de Polignac number, because 21870387217 - 2²⁷ = 21736169489 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21870387257) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 223167168 + ... + 223167265.

It is an arithmetic number, because the mean of its divisors is an integer number (4240177123).

Almost surely, 2^21870387217 is an apocalyptic number.

It is an amenable number.

21870387217 is a deficient number, since it is larger than the sum of its proper divisors (3570675521).

21870387217 is an equidigital number, since it uses as much as digits as its factorization.

21870387217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 446334447 (or 446334440 counting only the distinct ones).

The product of its (nonzero) digits is 263424, while the sum is 46.

The spelling of 21870387217 in words is "twenty-one billion, eight hundred seventy million, three hundred eighty-seven thousand, two hundred seventeen".