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A329898 a(n) is the position of 2*A025487(n) in A025487.

%I A329898 #18 Jan 12 2020 14:12:24
%S A329898 2,3,5,6,7,8,10,12,13,14,15,16,17,18,19,21,24,25,26,27,28,29,30,31,32,
%T A329898 33,34,35,36,37,39,40,42,45,46,47,48,49,50,51,52,53,55,56,57,58,59,60,
%U A329898 61,62,63,64,65,66,67,68,70,71,74,75,76,78,80,81,82,83,84,85,86,87,88,89,90,91,92,94,95,96,97,98,99,100
%N A329898 a(n) is the position of 2*A025487(n) in A025487.
%C A329898 Numbers k for which A007814(A025487(k)) > A007949(A025487(k)), i.e., numbers k for which the 2-adic valuation of A025487(k) is larger than its 3-adic valuation.
%C A329898 Numbers k for which A181815(k) is even.
%H A329898 Antti Karttunen, <a href="/A329898/b329898.txt">Table of n, a(n) for n = 1..10000</a>
%F A329898 For all n >= 1, A329904(a(n)) = n.
%t A329898 (* First, load the function f at A025487, then: *)
%t A329898 With[{s = Union@ Flatten@ f@ 6}, Map[If[2 # > Max@ s, Nothing, FirstPosition[s, 2 #][[1]] ] &, s]] (* _Michael De Vlieger_, Jan 11 2020 *)
%o A329898 (PARI)
%o A329898 upto_e = 64; \\ 64 -> 43608 terms.
%o A329898 A283980(n) = {my(f=factor(n)); prod(i=1, #f~, my(p=f[i, 1], e=f[i, 2]); if(p==2, 6, nextprime(p+1))^e)}; \\ From A283980
%o A329898 A329898list(e) = { my(lista = List([1, 2]), i=2, u = 2^e, t, v025487); while(lista[i] != u, if(2*lista[i] <= u, listput(lista,2*lista[i]); t =
%o A329898 A283980(lista[i]); if(t <= u, listput(lista,t))); i++); v025487 = vecsort(Vec(lista)); lista = List([]); for(i=1,oo,if(!(t=vecsearch(v025487,2*(v025487[i]))),return(Vec(lista)), listput(lista,t))); };
%o A329898 v329898 = A329898list(upto_e);
%o A329898 A329898(n) = v329898[n];
%Y A329898 Cf. A329897 (complement), A330683 (and its permutation).
%Y A329898 Cf. A007814, A007949, A025487, A329904 (a left inverse), A329906.
%Y A329898 Positions of even terms in A181815, zeros in A330682.
%K A329898 nonn
%O A329898 1,1
%A A329898 _Antti Karttunen_, Dec 24 2019