21377071681 has 9 divisors (see below), whose sum is σ = 24868396449. Its totient is φ = 18322327044.

The previous prime is 21377071679. The next prime is 21377071699. The reversal of 21377071681 is 18617077312.

It is a happy number.

The square root of 21377071681 is 146209.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 21377071681 - 2¹ = 21377071679 is a prime.

It is a super-2 number, since 2×21377071681² (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 (21377072681) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1013020 + ... + 1033906.

It is an arithmetic number, because the mean of its divisors is an integer number (2763155161).

Almost surely, 2^21377071681 is an apocalyptic number.

21377071681 is the 146209-th square number.

21377071681 is the 73105-th centered octagonal number.

It is an amenable number.

21377071681 is a deficient number, since it is larger than the sum of its proper divisors (3491324768).

21377071681 is an frugal number, since it uses more digits than its factorization.

21377071681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41788 (or 20894 counting only the distinct ones).

The product of its (nonzero) digits is 98784, while the sum is 43.

The spelling of 21377071681 in words is "twenty-one billion, three hundred seventy-seven million, seventy-one thousand, six hundred eighty-one".