21121347978 has 24 divisors (see below), whose sum is σ = 48454857828. Its totient is φ = 6626305152.

The previous prime is 21121347959. The next prime is 21121347979. The reversal of 21121347978 is 87974312112.

21121347978 is a `hidden beast` number, since 211 + 2 + 1 + 347 + 97 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 19958060529 + 1163287449 = 141273^2 + 34107^2 .

It is a super-2 number, since 2×21121347978² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21121347979) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 34511701 + ... + 34512312.

Almost surely, 2^21121347978 is an apocalyptic number.

21121347978 is an abundant number, since it is smaller than the sum of its proper divisors (27333509850).

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

21121347978 is a wasteful number, since it uses less digits than its factorization.

21121347978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69024038 (or 69024035 counting only the distinct ones).

The product of its digits is 169344, while the sum is 45.

The spelling of 21121347978 in words is "twenty-one billion, one hundred twenty-one million, three hundred forty-seven thousand, nine hundred seventy-eight".