261666421 has 2 divisors, whose sum is σ = 261666422. Its totient is φ = 261666420.

The previous prime is 261666413. The next prime is 261666439. The reversal of 261666421 is 124666162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 258759396 + 2907025 = 16086^2 + 1705^2 .

It is a cyclic number.

It is not a de Polignac number, because 261666421 - 2³ = 261666413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261666221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130833210 + 130833211.

It is an arithmetic number, because the mean of its divisors is an integer number (130833211).

Almost surely, 2^261666421 is an apocalyptic number.

It is an amenable number.

261666421 is a deficient number, since it is larger than the sum of its proper divisors (1).

261666421 is an equidigital number, since it uses as much as digits as its factorization.

261666421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 34.

The square root of 261666421 is about 16176.1064845654. The cubic root of 261666421 is about 639.6111089561.

The spelling of 261666421 in words is "two hundred sixty-one million, six hundred sixty-six thousand, four hundred twenty-one".