21655610401 has 2 divisors, whose sum is σ = 21655610402. Its totient is φ = 21655610400.

The previous prime is 21655610377. The next prime is 21655610407. The reversal of 21655610401 is 10401655612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13938163600 + 7717446801 = 118060^2 + 87849^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21655610401 is a prime.

It is not a weakly prime, because it can be changed into another prime (21655610407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10827805200 + 10827805201.

It is an arithmetic number, because the mean of its divisors is an integer number (10827805201).

Almost surely, 2^21655610401 is an apocalyptic number.

It is an amenable number.

21655610401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21655610401 is an equidigital number, since it uses as much as digits as its factorization.

21655610401 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7200, while the sum is 31.

The spelling of 21655610401 in words is "twenty-one billion, six hundred fifty-five million, six hundred ten thousand, four hundred one".