[seqfan] Re: a(n) and n have the same digitsum but no digit in common
David Wilson
davidwwilson at comcast.net
Wed Jan 5 01:38:11 CET 2011
Assuming digitsum actually means digital root, the least n >= 1 for which
a(n) is undefined is n = 1124578.
I figured this out in my head.
----- Original Message -----
From: "Eric Angelini" <Eric.Angelini at kntv.be>
To: "Sequence Fanatics Discussion list" <seqfan at list.seqfan.eu>
Sent: Tuesday, January 04, 2011 7:16 AM
Subject: [seqfan] a(n) and n have the same digitsum but no digit in common
Hello SeqFans,
n = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
25 26 27 28 29
S = 28,11,12,13,14,15,16,17,18,37, 2, 3, 4, 5, 6, 7, 8,
9,46,38,30,31,41,33,34,35,36, 1,...
S was built using always the smallest integer not yet present in S
such that a(n) and n have the same digitsum but no digit in common.
S is easy to compute by hand... in the beginning... but things quickly
become messy... Some help would be greatly appreciated!
S is finite: when it comes to n=1023456789 we are stuck for sure. But
S might stop with an earlier n: what would be the last term of S?
Best,
É.
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