PYHIYP means:
Put your hands in your pockets i.e. use no calculators, no pen & paper; just your eyes and you brain.
The 1st task, a harbinger to be followed by many others, is to prove just by observation and common sense that none of the four numbers listed below is a prime.
i. 5,234,567,896,743
ii. 1,438,525,775,258,341
iii. 77,112,356,378,491
iv. 1,431,436,216,211,339
No time limit!
No cheating!
KISS!
Post your conclusions.
Really? Nobody?
OK, here are the first two, which are easy:
(i) Sum of digits is divisible by 3, so the number is divisible by 3
(ii) This is a palindrome with an even number of digits, so it is divisible by 11. Or, if you prefer, the sum of the even digits less the sum odd digits is 0, which is divisible by 11, so the number is divisible by 11
Spoiler (i and ii)
