[seqfan] More stupid thingies with commas, sums & primes

Eric Angelini Eric.Angelini at kntv.be
Wed Oct 19 10:50:11 CEST 2011


Hello SeqFans,
a(n) is the smallest integer not yet present in S such that
the leftmost digit of a(n) and the rightmost digit of a(n-1)
sum up to a prime -- with a(1)=1.
S=1,2,3,4,7,6,5,8,9,20,21,10,22,11,12,13,23,24,14,15,25,26,16,...
(by hand)
I think S is a derangement of N.
Say a record of the successive "prime-sums" is kept [those sums
can only be equal to 2, 3, 5, 7, 11, 13 and 17]; will the fre-
quency of each sum slowly converge to 1/7th? 
Best,
É.








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