21780465209 has 2 divisors, whose sum is σ = 21780465210. Its totient is φ = 21780465208.

The previous prime is 21780465199. The next prime is 21780465241. The reversal of 21780465209 is 90256408712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20794505209 + 985960000 = 144203^2 + 31400^2 .

It is a cyclic number.

It is not a de Polignac number, because 21780465209 - 2²⁸ = 21512029753 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21780465209.

It is not a weakly prime, because it can be changed into another prime (21780465269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890232604 + 10890232605.

It is an arithmetic number, because the mean of its divisors is an integer number (10890232605).

Almost surely, 2^21780465209 is an apocalyptic number.

It is an amenable number.

21780465209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21780465209 is an equidigital number, since it uses as much as digits as its factorization.

21780465209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 241920, while the sum is 44.

The spelling of 21780465209 in words is "twenty-one billion, seven hundred eighty million, four hundred sixty-five thousand, two hundred nine".