64691640 has 192 divisors, whose sum is σ = 236658240. Its totient is φ = 15206400.

The previous prime is 64691639. The next prime is 64691657. The reversal of 64691640 is 4619646.

64691640 is a `hidden beast` number, since 6 + 4 + 6 + 9 + 1 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 64691595 and 64691604.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 107340 + ... + 107940.

It is an arithmetic number, because the mean of its divisors is an integer number (1232595).

Almost surely, 2^64691640 is an apocalyptic number.

64691640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 64691640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (118329120).

64691640 is an abundant number, since it is smaller than the sum of its proper divisors (171966600).

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

64691640 is a wasteful number, since it uses less digits than its factorization.

64691640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 654 (or 647 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 36.

The square root of 64691640 is about 8043.1113382820. Note that the first 3 decimals coincide. The cubic root of 64691640 is about 401.4357570052.

The spelling of 64691640 in words is "sixty-four million, six hundred ninety-one thousand, six hundred forty".