What links 3, 8, 19, 26 and 01631?

The Oban Times - - NEWS -

Two Oban High School pupils have won an Oban maths chal­lenge posed to the whole town.

The chal­lenge in­volved ‘ban’ num­bers: num­bers that do not con­tain a par­tic­u­lar let­ter when spelled out in English.

For ex­am­ple, all eban num­bers have the let­ter ‘e’ banned. The se­quence of eban num­bers starts 2, 4, 6, 30, 32, 34, 36, 40, 42, 44, 46, 50, 52, 54, 56, 60, 62, 64, 66, etc. All the num­bers are even.

Over the sum­mer hol­i­days, mys­te­ri­ous posters show­ing a se­quence of num­bers, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 23, 25, 26, and so on, were pinned up through­out the town, and read­ers were in­vited to guess what linked them all.

It took two Oban High School pupils, sec­ond-year Me­gan Day and sixth-year Caitlin Den­holme, to crack the code. They were the first to work out they are all oban num­bers, where the let­ter ‘o’ is banned. There are 454 oban num­bers. The Oban chal­lenge was set by Chris Smith, a teacher in Kil­marnock, who was in­spired by a talk about ban num­bers by Pro­fes­sor Adam McBride. They de­cided to pose the oban chal­lenge to the town, and found Oban High School maths teacher Iain Ma­cLean ready to help.

Me­gan and Caitlin each won a glass tro­phy and a £20 voucher.

Pro­fes­sor Adam McBride, Caitlin Den­holme, Iain Ma­cLean, Me­gan Day and Chris Smith.

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