21661013977 has 2 divisors, whose sum is σ = 21661013978. Its totient is φ = 21661013976.

The previous prime is 21661013867. The next prime is 21661014047. The reversal of 21661013977 is 77931016612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11789399241 + 9871614736 = 108579^2 + 99356^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661013977 - 2⁷ = 21661013849 is a prime.

It is not a weakly prime, because it can be changed into another prime (21661013677) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830506988 + 10830506989.

It is an arithmetic number, because the mean of its divisors is an integer number (10830506989).

Almost surely, 2^21661013977 is an apocalyptic number.

It is an amenable number.

21661013977 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661013977 is an equidigital number, since it uses as much as digits as its factorization.

21661013977 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 95256, while the sum is 43.

The spelling of 21661013977 in words is "twenty-one billion, six hundred sixty-one million, thirteen thousand, nine hundred seventy-seven".