2020
This number is a composite.
The dystopian future-fiction novel Nineteen
Eighty-Four was submitted for publication in December
of 1948. The full span is p12 years, while with
emirp partner p21 the span would instead be
through 2020. [Merickel]
(2020)47120 * 2^20202 - 1 is prime. [Noll]
For three composite years y-1, y, and y+1 the prime
factorization of y has no digits in common with the prime
factorizations of y-1 or y+1 for y=2020. The last three
years with this property were 1815, 1935, and 2019. The
next three such years will be 2045, 2049, and 2065. [Gaydos]
Our current calendar year, 2020, may be computed with the
same "formula" by using any of the one-digit primes (2, 3, 5
and 7), one at a time, as shown:
2020 = {[(dddd-dd)*dd]/(d+d)+dd-d}/(d+d+d) =
{[(2222-22)*22]/(2+2)+22-2}/(2+2+2) =
{[(3333-33)*33]/(3+3)+33-3}/(3+3+3) =
{[(5555-55)*55]/(5+5)+55-5}/(5+5+5) =
{[(7777-77)*77]/(7+7)+77-7}/(7+7+7). [Rivera]