261777581 has 8 divisors (see below), whose sum is σ = 282109464. Its totient is φ = 241473600.

The previous prime is 261777541. The next prime is 261777583. The reversal of 261777581 is 185777162.

It can be written as a sum of positive squares in 4 ways, for example, as 8649481 + 253128100 = 2941^2 + 15910^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261777581 is a prime.

It is a super-2 number, since 2×261777581² = 137055003828423122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261777583) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15131 + ... + 27431.

It is an arithmetic number, because the mean of its divisors is an integer number (35263683).

Almost surely, 2^261777581 is an apocalyptic number.

It is an amenable number.

261777581 is a deficient number, since it is larger than the sum of its proper divisors (20331883).

261777581 is a wasteful number, since it uses less digits than its factorization.

261777581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13951.

The product of its digits is 164640, while the sum is 44.

The square root of 261777581 is about 16179.5420516157. The cubic root of 261777581 is about 639.7016684108.

The spelling of 261777581 in words is "two hundred sixty-one million, seven hundred seventy-seven thousand, five hundred eighty-one".