21605162640749 has 2 divisors, whose sum is σ = 21605162640750. Its totient is φ = 21605162640748.

The previous prime is 21605162640739. The next prime is 21605162640767. The reversal of 21605162640749 is 94704626150612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20256138465124 + 1349024175625 = 4500682^2 + 1161475^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21605162640749 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21605162640749.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21605162640739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802581320374 + 10802581320375.

It is an arithmetic number, because the mean of its divisors is an integer number (10802581320375).

Almost surely, 2^{21605162640749} is an apocalyptic number.

It is an amenable number.

21605162640749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605162640749 is an equidigital number, since it uses as much as digits as its factorization.

21605162640749 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4354560, while the sum is 53.

The spelling of 21605162640749 in words is "twenty-one trillion, six hundred five billion, one hundred sixty-two million, six hundred forty thousand, seven hundred forty-nine".