661899986261 has 2 divisors, whose sum is σ = 661899986262. Its totient is φ = 661899986260.

The previous prime is 661899986221. The next prime is 661899986269. The reversal of 661899986261 is 162689998166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 585961161361 + 75938824900 = 765481^2 + 275570^2 .

It is a cyclic number.

It is not a de Polignac number, because 661899986261 - 2³⁸ = 387022079317 is a prime.

It is a super-2 number, since 2×661899986261² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661899986269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330949993130 + 330949993131.

It is an arithmetic number, because the mean of its divisors is an integer number (330949993131).

Almost surely, 2^661899986261 is an apocalyptic number.

It is an amenable number.

661899986261 is a deficient number, since it is larger than the sum of its proper divisors (1).

661899986261 is an equidigital number, since it uses as much as digits as its factorization.

661899986261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 120932352, while the sum is 71.

The spelling of 661899986261 in words is "six hundred sixty-one billion, eight hundred ninety-nine million, nine hundred eighty-six thousand, two hundred sixty-one".