Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #17 Dec 15 2023 11:39:08
%S 1,2,2,3,3,5,5,7,7,7,7,11,11,13,13,13,14,17,17,19,19,19,19,23,23,23,
%T 23,23,26,29,29,31,31,31,31,31,34,37,37,37,38,41,41,43,43,43,43,47,47,
%U 47,47,47,47,53,53,53,53,53
%N For n >= 7, max(A151799(n), 2*A151799(floor((n-1)/2))).
%D S. K. Stein and S. Szabo, Algebra and Tiling, MAA Carus Monograph 25, 1994, page 104.
%H Robert Israel, <a href="/A035031/b035031.txt">Table of n, a(n) for n = 1..10000</a>
%p f:= proc(n) max(prevprime(n), 2*prevprime(floor((n-1)/2))) end proc:
%p for i from 1 to 6 do f(i):= [1, 2, 2, 3, 3, 5, 5][i] od:
%p map(f, [$1..100]); # _Robert Israel_, Dec 15 2023
%t Join[{1,2},Table[Max[NextPrime[n,-1],2NextPrime[Floor[(n-1)/2],-1]],{n,3,70}]] (* _Harvey P. Dale_, Mar 12 2022 *)
%Y Cf. A035032, A151799.
%K nonn
%O 1,2
%A _N. J. A. Sloane_