261663641 has 2 divisors, whose sum is σ = 261663642. Its totient is φ = 261663640.

The previous prime is 261663637. The next prime is 261663671. The reversal of 261663641 is 146366162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 250747225 + 10916416 = 15835^2 + 3304^2 .

It is a cyclic number.

It is not a de Polignac number, because 261663641 - 2² = 261663637 is a prime.

It is a super-2 number, since 2×261663641² = 136935722042753762, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (261663601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130831820 + 130831821.

It is an arithmetic number, because the mean of its divisors is an integer number (130831821).

Almost surely, 2^261663641 is an apocalyptic number.

It is an amenable number.

261663641 is a deficient number, since it is larger than the sum of its proper divisors (1).

261663641 is an equidigital number, since it uses as much as digits as its factorization.

261663641 is an evil number, because the sum of its binary digits is even.

The product of its digits is 31104, while the sum is 35.

The square root of 261663641 is about 16176.0205551304. The cubic root of 261663641 is about 639.6088438263.

The spelling of 261663641 in words is "two hundred sixty-one million, six hundred sixty-three thousand, six hundred forty-one".