6561921941 has 2 divisors, whose sum is σ = 6561921942. Its totient is φ = 6561921940.

The previous prime is 6561921929. The next prime is 6561922007. The reversal of 6561921941 is 1491291656.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6283732900 + 278189041 = 79270^2 + 16679^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6561921941 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 6561921892 and 6561921901.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6561941941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3280960970 + 3280960971.

It is an arithmetic number, because the mean of its divisors is an integer number (3280960971).

Almost surely, 2^6561921941 is an apocalyptic number.

It is an amenable number.

6561921941 is a deficient number, since it is larger than the sum of its proper divisors (1).

6561921941 is an equidigital number, since it uses as much as digits as its factorization.

6561921941 is an evil number, because the sum of its binary digits is even.

The product of its digits is 116640, while the sum is 44.

The square root of 6561921941 is about 81005.6907939189. The cubic root of 6561921941 is about 1872.1631236339.

The spelling of 6561921941 in words is "six billion, five hundred sixty-one million, nine hundred twenty-one thousand, nine hundred forty-one".