661585397641 has 27 divisors (see below), whose sum is σ = 776394292557. Its totient is φ = 562109959320.

The previous prime is 661585397591. The next prime is 661585397657. The reversal of 661585397641 is 146793585166.

It is a happy number.

The square root of 661585397641 is 813379.

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

It is not a de Polignac number, because 661585397641 - 2¹¹ = 661585395593 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 661585397641.

It is not an unprimeable number, because it can be changed into a prime (661585397041) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 745868100 + ... + 745868986.

Almost surely, 2^661585397641 is an apocalyptic number.

661585397641 is the 813379-th square number.

661585397641 is the 406690-th centered octagonal number.

It is an amenable number.

661585397641 is a deficient number, since it is larger than the sum of its proper divisors (114808894916).

661585397641 is an frugal number, since it uses more digits than its factorization.

661585397641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2050 (or 1025 counting only the distinct ones).

The product of its digits is 32659200, while the sum is 61.

The spelling of 661585397641 in words is "six hundred sixty-one billion, five hundred eighty-five million, three hundred ninety-seven thousand, six hundred forty-one".