"Extraordinary!" you exclaim when Sam shows you the answer. (See " RATS! I Have No Clue. ")
"Of course," Sam whispers, "this is not the only such sequence possible."
"Sam, maybe another time. I'm feeling a bit tired..."
"No, wait!" He scribbles another sequence down:
"Sam! I said I was tired!"
"Not so much. You see, you almost just told me the rule," says Sam, a sly smile on his face.
What is the next term?
Bonus: What is the rule?
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"Sam" is actually an anagram of the acronym for the rule: S eparate, M ultiply, A dd. The proper name for these sequences is Digit Product Sequences .
1 : Separate the term into its digits (i.e. 4 5 becomes 4 , 5 ).
2 : Multiply the non-zero digits together (i.e. 4 5 → ( 4 , 5 ) → 4 ∗ 5 = 2 0 ).
3 : Add the resulting product of digits to the original term (i.e. 2 0 + 4 5 = 6 5 ).
In a nutshell, add the product of the digits of a n − 1 to a n − 1 to obtain a n .
Note: Notice that when we start with a seed value a 0 = 3 , we obtain the sequence
3 , 6 , 1 4 , 1 8 , 2 6 . . .
This sequence 'meets up' with the sequence started by the seed value A 0 = 1 at a 4 and A 7 . It has been conjectured that this 'meeting up' behavior of the Digit Product Sequence occurs for every pair of seed values.
Credit : Paul Loomis, An Interesting Family of Iterated Sequences