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.
Of the positive integers (4,5,7,8,9,10,11,...) not among the first 4 terms of the sequence, 10 is the smallest which is divisible by a different number of distinct primes than a(4) = 3. So a(5) = 10.
import Data.List (delete)
a109465 n = a109465_list !! (n-1)
a109465_list = f 1 [1..] where
f o xs = g xs where
g (z:zs) = if o' == o then g zs else z : f o' (delete z xs)
where o' = a001221 z
-- Reinhard Zumkeller, Aug 07 2014
a = {1}; Do[k = 2; While[Nand[FreeQ[a, k], PrimeNu[k] != PrimeNu[a[[i - 1]]]], k++]; AppendTo[a, k], {i, 2, 72}]; a (* Michael De Vlieger, Sep 28 2017 *)
import Data.List (elemIndex); import Data.Maybe (fromJust) a243692 = (+ 1) . fromJust . (`elemIndex` a143691_list) -- Reinhard Zumkeller, Aug 07 2014
N:= 1000: # to get a(1) to a(N) Odds,Evens:= selectremove(t -> numtheory:-bigomega(t)::odd,[$1..N]): for k from 1 to nops(Odds) do A[Odds[k]]:= 2*k od: for k from 1 to nops(Evens) do A[Evens[k]]:= 2*k-1 od: seq(A[k],k=1..N); # Robert Israel, Jul 27 2014
m = 100;
odds = Select[Range[m], OddQ[PrimeOmega[#]]&];
evens = Select[Range[m], EvenQ[PrimeOmega[#]]&];
Do[a[odds[[k]]] = 2k, {k, 1, Length[odds]}];
Do[a[evens[[k]]] = 2k-1, {k, 1, Length[evens]}];
Array[a, m] (* Jean-François Alcover, Mar 09 2019, from Maple *)
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