21661246561601 has 2 divisors, whose sum is σ = 21661246561602. Its totient is φ = 21661246561600.

The previous prime is 21661246561597. The next prime is 21661246561609. The reversal of 21661246561601 is 10616564216612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17277331873201 + 4383914688400 = 4156601^2 + 2093780^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661246561601 - 2² = 21661246561597 is a prime.

It is a super-2 number, since 2×21661246561601² (a number of 27 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21661246561609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830623280800 + 10830623280801.

It is an arithmetic number, because the mean of its divisors is an integer number (10830623280801).

Almost surely, 2^{21661246561601} is an apocalyptic number.

It is an amenable number.

21661246561601 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661246561601 is an equidigital number, since it uses as much as digits as its factorization.

21661246561601 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 622080, while the sum is 47.

The spelling of 21661246561601 in words is "twenty-one trillion, six hundred sixty-one billion, two hundred forty-six million, five hundred sixty-one thousand, six hundred one".