This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A173979 #14 Oct 25 2024 06:29:58
%S A173979 5,13,25,127,85,196,181,472,421,946,685,1210,925,1105,1882,3157,1861,
%T A173979 2446,2521,3541,4306,4690,3961,6160,5707,5305,5725,6922,9436,8065,
%U A173979 8581,10207,9661,13336,12307,12796,14752,18955,14965
%N A173979 a(n) is the smallest number m from A173977 for which A020639(2m-1) = prime(n).
%C A173979 If the requirement that m be an element of A173977 is dropped, the sequence becomes A006254. - _R. J. Mathar_, Nov 02 2011
%H A173979 Amiram Eldar, <a href="/A173979/b173979.txt">Table of n, a(n) for n = 2..1000</a>
%p A173979 A020639 := proc(n) if n = 1 then 1; else min(op(numtheory[factorset](n)) ) ; end if; end proc:
%p A173979 isA173977 := proc(n) A020639(2*n-1) < A020639(2*n-3) ; end proc:
%p A173979 A173979 := proc(n) local p,m ; p := ithprime(n) ; for m from 1 do if A020639(2*m-1) = p and isA173977(m) then return m ; end if; end do: end proc:
%p A173979 seq(A173979(n),n=2..40) ; # _R. J. Mathar_, Sep 02 2011
%t A173979 lpf[n_] := lpf[n] = FactorInteger[n][[1, 1]]; q[n_] := lpf[2*n-1] < lpf[2*n-3]; seq[len_] := Module[{s = Table[0, {Prime[len+1]}], k = 2, c = 0, p}, While[c < len, If[q[k], p = lpf[2*k-1]; If[p <= Length[s] && s[[p]] == 0, c++; s[[p]] = k]]; k++]; Select[s, # > 0 &]]; seq[100] (* _Amiram Eldar_, Oct 25 2024 *)
%Y A173979 Cf. A006254, A020639, A173977.
%K A173979 nonn
%O A173979 2,1
%A A173979 _Vladimir Shevelev_, Mar 04 2010
%E A173979 Name corrected by _Vladimir Shevelev_, Mar 15 2010