261501781 has 2 divisors, whose sum is σ = 261501782. Its totient is φ = 261501780.

The previous prime is 261501767. The next prime is 261501811. The reversal of 261501781 is 187105162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 254689681 + 6812100 = 15959^2 + 2610^2 .

It is a cyclic number.

It is not a de Polignac number, because 261501781 - 2⁹ = 261501269 is a prime.

It is a super-2 number, since 2×261501781² = 136766362932343922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261501181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130750890 + 130750891.

It is an arithmetic number, because the mean of its divisors is an integer number (130750891).

Almost surely, 2^261501781 is an apocalyptic number.

It is an amenable number.

261501781 is a deficient number, since it is larger than the sum of its proper divisors (1).

261501781 is an equidigital number, since it uses as much as digits as its factorization.

261501781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3360, while the sum is 31.

The square root of 261501781 is about 16171.0166965469. The cubic root of 261501781 is about 639.4769334585.

The spelling of 261501781 in words is "two hundred sixty-one million, five hundred one thousand, seven hundred eighty-one".