21715855387787 has 16 divisors (see below), whose sum is σ = 23793487990272. Its totient is φ = 19655551297920.

The previous prime is 21715855387771. The next prime is 21715855387801. The reversal of 21715855387787 is 78778355851712.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21715855387787 - 2⁴ = 21715855387771 is a prime.

It is a super-2 number, since 2×21715855387787² (a number of 27 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21715855387747) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3028778 + ... + 7252944.

It is an arithmetic number, because the mean of its divisors is an integer number (1487092999392).

Almost surely, 2^{21715855387787} is an apocalyptic number.

21715855387787 is a deficient number, since it is larger than the sum of its proper divisors (2077632602485).

21715855387787 is a wasteful number, since it uses less digits than its factorization.

21715855387787 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4226218.

The product of its digits is 921984000, while the sum is 74.

The spelling of 21715855387787 in words is "twenty-one trillion, seven hundred fifteen billion, eight hundred fifty-five million, three hundred eighty-seven thousand, seven hundred eighty-seven".