617978921 has 24 divisors (see below), whose sum is σ = 738843840. Its totient is φ = 506181312.

The previous prime is 617978909. The next prime is 617978923. The reversal of 617978921 is 129879716.

617978921 = T₄₆₉ + T₄₇₀ + ... + T₁₅₆₁.

It is not a de Polignac number, because 617978921 - 2²² = 613784617 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 617978921.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (617978923) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 564851 + ... + 565943.

It is an arithmetic number, because the mean of its divisors is an integer number (30785160).

Almost surely, 2^617978921 is an apocalyptic number.

It is an amenable number.

617978921 is a deficient number, since it is larger than the sum of its proper divisors (120864919).

617978921 is a wasteful number, since it uses less digits than its factorization.

617978921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1233 (or 1196 counting only the distinct ones).

The product of its digits is 381024, while the sum is 50.

The square root of 617978921 is about 24859.1818248308. The cubic root of 617978921 is about 851.7743424551.

The spelling of 617978921 in words is "six hundred seventeen million, nine hundred seventy-eight thousand, nine hundred twenty-one".