667661221 has 2 divisors, whose sum is σ = 667661222. Its totient is φ = 667661220.

The previous prime is 667661201. The next prime is 667661233. The reversal of 667661221 is 122166766.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 664092900 + 3568321 = 25770^2 + 1889^2 .

It is a cyclic number.

It is not a de Polignac number, because 667661221 - 2¹³ = 667653029 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (667661201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333830610 + 333830611.

It is an arithmetic number, because the mean of its divisors is an integer number (333830611).

Almost surely, 2^667661221 is an apocalyptic number.

It is an amenable number.

667661221 is a deficient number, since it is larger than the sum of its proper divisors (1).

667661221 is an equidigital number, since it uses as much as digits as its factorization.

667661221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 37.

The square root of 667661221 is about 25839.1412589505. The cubic root of 667661221 is about 874.0146605105.

The spelling of 667661221 in words is "six hundred sixty-seven million, six hundred sixty-one thousand, two hundred twenty-one".