21256645477 has 2 divisors, whose sum is σ = 21256645478. Its totient is φ = 21256645476.

The previous prime is 21256645381. The next prime is 21256645481. The reversal of 21256645477 is 77454665212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14676353316 + 6580292161 = 121146^2 + 81119^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21256645477 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21256645477.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256655477) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628322738 + 10628322739.

It is an arithmetic number, because the mean of its divisors is an integer number (10628322739).

Almost surely, 2^21256645477 is an apocalyptic number.

It is an amenable number.

21256645477 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256645477 is an equidigital number, since it uses as much as digits as its factorization.

21256645477 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2822400, while the sum is 49.

The spelling of 21256645477 in words is "twenty-one billion, two hundred fifty-six million, six hundred forty-five thousand, four hundred seventy-seven".