661411721 has 2 divisors, whose sum is σ = 661411722. Its totient is φ = 661411720.

The previous prime is 661411661. The next prime is 661411757. The reversal of 661411721 is 127114166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 497290000 + 164121721 = 22300^2 + 12811^2 .

It is a cyclic number.

It is not a de Polignac number, because 661411721 - 2⁶ = 661411657 is a prime.

It is not a weakly prime, because it can be changed into another prime (661411781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330705860 + 330705861.

It is an arithmetic number, because the mean of its divisors is an integer number (330705861).

Almost surely, 2^661411721 is an apocalyptic number.

It is an amenable number.

661411721 is a deficient number, since it is larger than the sum of its proper divisors (1).

661411721 is an equidigital number, since it uses as much as digits as its factorization.

661411721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2016, while the sum is 29.

The square root of 661411721 is about 25717.9260633512. The cubic root of 661411721 is about 871.2790983861.

Adding to 661411721 its reverse (127114166), we get a palindrome (788525887).

The spelling of 661411721 in words is "six hundred sixty-one million, four hundred eleven thousand, seven hundred twenty-one".