1261821390 has 16 divisors (see below), whose sum is σ = 3028371408. Its totient is φ = 336485696.

The previous prime is 1261821359. The next prime is 1261821401. The reversal of 1261821390 is 931281621.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21030327 + ... + 21030386.

It is an arithmetic number, because the mean of its divisors is an integer number (189273213).

Almost surely, 2^1261821390 is an apocalyptic number.

1261821390 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

1261821390 is an abundant number, since it is smaller than the sum of its proper divisors (1766550018).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1261821390 is a wasteful number, since it uses less digits than its factorization.

1261821390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42060723.

The product of its (nonzero) digits is 5184, while the sum is 33.

The square root of 1261821390 is about 35522.1253587113. The cubic root of 1261821390 is about 1080.6024844826.

The spelling of 1261821390 in words is "one billion, two hundred sixty-one million, eight hundred twenty-one thousand, three hundred ninety".