128401661 has 2 divisors, whose sum is σ = 128401662. Its totient is φ = 128401660.

The previous prime is 128401657. The next prime is 128401687. The reversal of 128401661 is 166104821.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 128368900 + 32761 = 11330^2 + 181^2 .

It is a cyclic number.

It is not a de Polignac number, because 128401661 - 2² = 128401657 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (128401631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64200830 + 64200831.

It is an arithmetic number, because the mean of its divisors is an integer number (64200831).

Almost surely, 2^128401661 is an apocalyptic number.

It is an amenable number.

128401661 is a deficient number, since it is larger than the sum of its proper divisors (1).

128401661 is an equidigital number, since it uses as much as digits as its factorization.

128401661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 128401661 is about 11331.4456712284. The cubic root of 128401661 is about 504.4950165555.

The spelling of 128401661 in words is "one hundred twenty-eight million, four hundred one thousand, six hundred sixty-one".