661981389542001 has 9 divisors (see below), whose sum is σ = 956195451941899. Its totient is φ = 441320874903336.

The previous prime is 661981389541999. The next prime is 661981389542027. The reversal of 661981389542001 is 100245983189166.

The square root of 661981389542001 is 25728999.

It is a perfect power (a square), and thus also a powerful number.

661981389542001 is a `hidden beast` number, since 6 + 6 + 1 + 9 + 8 + 1 + 3 + 89 + 542 + 0 + 0 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 480387545885025 + 181593843656976 = 21917745^2 + 13475676^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 661981389542001 - 2¹ = 661981389541999 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661981389542001.

It is not an unprimeable number, because it can be changed into a prime (661981389542801) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 72898831 + ... + 81475163.

Almost surely, 2^{661981389542001} is an apocalyptic number.

661981389542001 is the 25728999-th square number.

661981389542001 is the 12864500-th centered octagonal number.

It is an amenable number.

661981389542001 is a deficient number, since it is larger than the sum of its proper divisors (294214062399898).

661981389542001 is an frugal number, since it uses more digits than its factorization.

661981389542001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17152672 (or 8576336 counting only the distinct ones).

The product of its (nonzero) digits is 22394880, while the sum is 63.

The spelling of 661981389542001 in words is "six hundred sixty-one trillion, nine hundred eighty-one billion, three hundred eighty-nine million, five hundred forty-two thousand, one".