666345251621 has 4 divisors (see below), whose sum is σ = 761537430432. Its totient is φ = 571153072812.

The previous prime is 666345251603. The next prime is 666345251633. The reversal of 666345251621 is 126152543666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 126152543666 = 2 ⋅63076271833.

It is not a de Polignac number, because 666345251621 - 2¹⁸ = 666344989477 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666345251641) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47596089395 + ... + 47596089408.

It is an arithmetic number, because the mean of its divisors is an integer number (190384357608).

Almost surely, 2^666345251621 is an apocalyptic number.

It is an amenable number.

666345251621 is a deficient number, since it is larger than the sum of its proper divisors (95192178811).

666345251621 is an equidigital number, since it uses as much as digits as its factorization.

666345251621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95192178810.

The product of its digits is 1555200, while the sum is 47.

The spelling of 666345251621 in words is "six hundred sixty-six billion, three hundred forty-five million, two hundred fifty-one thousand, six hundred twenty-one".