21305720077 has 2 divisors, whose sum is σ = 21305720078. Its totient is φ = 21305720076.

The previous prime is 21305720063. The next prime is 21305720113. The reversal of 21305720077 is 77002750312.

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., 15429117796 + 5876602281 = 124214^2 + 76659^2 .

It is a cyclic number.

It is not a de Polignac number, because 21305720077 - 2⁷ = 21305719949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21305720017) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10652860038 + 10652860039.

It is an arithmetic number, because the mean of its divisors is an integer number (10652860039).

Almost surely, 2^21305720077 is an apocalyptic number.

It is an amenable number.

21305720077 is a deficient number, since it is larger than the sum of its proper divisors (1).

21305720077 is an equidigital number, since it uses as much as digits as its factorization.

21305720077 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20580, while the sum is 34.

The spelling of 21305720077 in words is "twenty-one billion, three hundred five million, seven hundred twenty thousand, seventy-seven".