21977923661 has 2 divisors, whose sum is σ = 21977923662. Its totient is φ = 21977923660.

The previous prime is 21977923619. The next prime is 21977923687. The reversal of 21977923661 is 16632977912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21511795561 + 466128100 = 146669^2 + 21590^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21977923661 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21977923601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10988961830 + 10988961831.

It is an arithmetic number, because the mean of its divisors is an integer number (10988961831).

Almost surely, 2^21977923661 is an apocalyptic number.

It is an amenable number.

21977923661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21977923661 is an equidigital number, since it uses as much as digits as its factorization.

21977923661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1714608, while the sum is 53.

The spelling of 21977923661 in words is "twenty-one billion, nine hundred seventy-seven million, nine hundred twenty-three thousand, six hundred sixty-one".