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4

If 12 - 13 year primary school student doesn't know algebra & it recognise pattern in math - develop divisibility test then yes it is invention for him. Is it new discovery in math ? No. Test given by Chika is too old. It is also in BKT's 'Vedic Mathematics' book - Published in 1965. I had given general Theorem (called Cross Divisibility Theorem) to ...


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This and related divisibility tests are ancient and well-known to most who have mastered a first course in elementary number theory. They go back at least a couple hundred years, and possibly even much further (e.g. possibly to circa 1200 given Leonardo Pisano (b.k.a. Fibonacci) discussed tests for divisibility by 7,9,11 in his Liber Abaci (Book of ...


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This was published in 1965 as rule no 2 for divisibility by 7 in Vedic Maths. Here’s a blog post from 2009 about it http://blogannath.blogspot.com/2009/10/vedic-mathematics-lesson-23.html?m=1 Edit: here’s a Wikipedia link showing Vedic Maths was published in 1965. https://en.m.wikipedia.org/wiki/Vedic_Maths


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The Math.SE question about the method (Why does Chika Ofili's method for checking divisibility for 7 work?) is closed as a duplicate of an earlier, more generic, question (Divisibility criteria for 7,11,13,17,19) about divisibility tests for various prime numbers. The answer by @VitthalJadhav, posted back in 2013 includes Chica Ofili's formula verbatim: (...


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