21197827661 has 2 divisors, whose sum is σ = 21197827662. Its totient is φ = 21197827660.

The previous prime is 21197827597. The next prime is 21197827757. The reversal of 21197827661 is 16672879112.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12277969636 + 8919858025 = 110806^2 + 94445^2 .

It is a cyclic number.

It is not a de Polignac number, because 21197827661 - 2⁶ = 21197827597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21197827061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10598913830 + 10598913831.

It is an arithmetic number, because the mean of its divisors is an integer number (10598913831).

Almost surely, 2^21197827661 is an apocalyptic number.

It is an amenable number.

21197827661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21197827661 is an equidigital number, since it uses as much as digits as its factorization.

21197827661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 508032, while the sum is 50.

The spelling of 21197827661 in words is "twenty-one billion, one hundred ninety-seven million, eight hundred twenty-seven thousand, six hundred sixty-one".