21390007761 has 6 divisors (see below), whose sum is σ = 30896677890. Its totient is φ = 14260005168.

The previous prime is 21390007759. The next prime is 21390007799. The reversal of 21390007761 is 16770009312.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 16893500625 + 4496507136 = 129975^2 + 67056^2 .

It is not a de Polignac number, because 21390007761 - 2¹ = 21390007759 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21390006761) 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, 1188333756 + ... + 1188333773.

It is an arithmetic number, because the mean of its divisors is an integer number (5149446315).

Almost surely, 2^21390007761 is an apocalyptic number.

It is an amenable number.

21390007761 is a deficient number, since it is larger than the sum of its proper divisors (9506670129).

21390007761 is a wasteful number, since it uses less digits than its factorization.

21390007761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376667535 (or 2376667532 counting only the distinct ones).

The product of its (nonzero) digits is 15876, while the sum is 36.

The spelling of 21390007761 in words is "twenty-one billion, three hundred ninety million, seven thousand, seven hundred sixty-one".