661989071 has 2 divisors, whose sum is σ = 661989072. Its totient is φ = 661989070.

The previous prime is 661989007. The next prime is 661989091. The reversal of 661989071 is 170989166.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 661989071 - 2⁶ = 661989007 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661989091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330994535 + 330994536.

It is an arithmetic number, because the mean of its divisors is an integer number (330994536).

Almost surely, 2^661989071 is an apocalyptic number.

661989071 is a deficient number, since it is larger than the sum of its proper divisors (1).

661989071 is an equidigital number, since it uses as much as digits as its factorization.

661989071 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 163296, while the sum is 47.

The square root of 661989071 is about 25729.1482758369. The cubic root of 661989071 is about 871.5325394606.

The spelling of 661989071 in words is "six hundred sixty-one million, nine hundred eighty-nine thousand, seventy-one".