261818551 has 2 divisors, whose sum is σ = 261818552. Its totient is φ = 261818550.

The previous prime is 261818489. The next prime is 261818597. The reversal of 261818551 is 155818162.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261818551 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 261818551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261810551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130909275 + 130909276.

It is an arithmetic number, because the mean of its divisors is an integer number (130909276).

Almost surely, 2^261818551 is an apocalyptic number.

261818551 is a deficient number, since it is larger than the sum of its proper divisors (1).

261818551 is an equidigital number, since it uses as much as digits as its factorization.

261818551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 19200, while the sum is 37.

The square root of 261818551 is about 16180.8081071373. The cubic root of 261818551 is about 639.7350392469.

The spelling of 261818551 in words is "two hundred sixty-one million, eight hundred eighteen thousand, five hundred fifty-one".