661398121 has 2 divisors, whose sum is σ = 661398122. Its totient is φ = 661398120.

The previous prime is 661398119. The next prime is 661398149. The reversal of 661398121 is 121893166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 576960400 + 84437721 = 24020^2 + 9189^2 .

It is a cyclic number.

It is not a de Polignac number, because 661398121 - 2¹ = 661398119 is a prime.

Together with 661398119, it forms a pair of twin primes.

It is equal to p_34355098 and since 661398121 and 34355098 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (661398161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330699060 + 330699061.

It is an arithmetic number, because the mean of its divisors is an integer number (330699061).

Almost surely, 2^661398121 is an apocalyptic number.

It is an amenable number.

661398121 is a deficient number, since it is larger than the sum of its proper divisors (1).

661398121 is an equidigital number, since it uses as much as digits as its factorization.

661398121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 37.

The square root of 661398121 is about 25717.6616549794. The cubic root of 661398121 is about 871.2731265753.

The spelling of 661398121 in words is "six hundred sixty-one million, three hundred ninety-eight thousand, one hundred twenty-one".