21661465666921 has 2 divisors, whose sum is σ = 21661465666922. Its totient is φ = 21661465666920.

The previous prime is 21661465666891. The next prime is 21661465666933. The reversal of 21661465666921 is 12966656416612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16065378650896 + 5596087016025 = 4008164^2 + 2365605^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661465666921 - 2³¹ = 21659318183273 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21661465666921.

It is not a weakly prime, because it can be changed into another prime (21661465666961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830732833460 + 10830732833461.

It is an arithmetic number, because the mean of its divisors is an integer number (10830732833461).

Almost surely, 2^{21661465666921} is an apocalyptic number.

It is an amenable number.

21661465666921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661465666921 is an equidigital number, since it uses as much as digits as its factorization.

21661465666921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 33592320, while the sum is 61.

The spelling of 21661465666921 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred sixty-five million, six hundred sixty-six thousand, nine hundred twenty-one".