perplexus.info :: Just Math : Find that decade

Find that decade (Posted on 2014-01-06)

There has been only a single instance in the course of American history (1776 AD onwards) wherein there was a decade in which four of the years were prime numbers. Find that decade.

Submitted by K Sengupta

Rating: 5.0000 (1 votes)

Solution: (Hide)

1871, 1873, 1877, 1879 --were prime years.*
*btw ,exactly twenty years LATER 1891, 1893, 1895, 1897, 1899, were ALL composite!!
(it will happen again in 2081, 2083 ,2087, 2089),+
exactly twenty years LATER 2101,2103,2105,2107 &2109 will be ALL composite!!

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
re(2): Look Ma, no primes!	Steve Herman	2014-01-06 19:39:23
re: Look Ma, no primes!	Ady TZIDON	2014-01-06 14:36:19
Look Ma, no primes!	Steve Herman	2014-01-06 14:09:02
spoiler	Ady TZIDON	2014-01-06 10:18:21

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