661721501266 has 24 divisors (see below), whose sum is σ = 1179203239296. Its totient is φ = 277560992520.

The previous prime is 661721501191. The next prime is 661721501267. The reversal of 661721501266 is 662105127166.

It is not an unprimeable number, because it can be changed into a prime (661721501267) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 71827950 + ... + 71837161.

It is an arithmetic number, because the mean of its divisors is an integer number (49133468304).

Almost surely, 2^661721501266 is an apocalyptic number.

661721501266 is a deficient number, since it is larger than the sum of its proper divisors (517481738030).

661721501266 is a wasteful number, since it uses less digits than its factorization.

661721501266 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 143665174 (or 143665167 counting only the distinct ones).

The product of its (nonzero) digits is 181440, while the sum is 43.

The spelling of 661721501266 in words is "six hundred sixty-one billion, seven hundred twenty-one million, five hundred one thousand, two hundred sixty-six".