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A266409 a(n) = (A003309(n+2)-1) / 2; numbers n such that 2n+1 is a Ludic number (in A003309).

%I A266409 #9 Jan 30 2016 03:09:26
%S A266409 1,2,3,5,6,8,11,12,14,18,20,21,23,26,30,33,35,38,41,44,45,48,53,57,59,
%T A266409 60,63,65,71,74,78,80,86,87,89,90,96,104,105,110,111,113,116,117,119,
%U A266409 123,128,132,138,141,143,150,153,156,164,165,168,170,176,179,180,188,191,194,198,203,207,209,210,215
%N A266409 a(n) = (A003309(n+2)-1) / 2; numbers n such that 2n+1 is a Ludic number (in A003309).
%C A266409 Ludic numbers from A003309(2) = 3 onward, decremented by one, then halved.
%H A266409 Antti Karttunen, <a href="/A266409/b266409.txt">Table of n, a(n) for n = 1..10226</a>
%F A266409 a(n) = (A003309(n+2)-1) / 2.
%F A266409 Other identities. For all n >= 1:
%F A266409 A266350(a(n)) = n.
%o A266409 (Scheme, two versions)
%o A266409 (define (A266409 n) (/ (- (A003309 (+ 2 n)) 1) 2))
%o A266409 (define A266409 (NONZERO-POS 1 1 (lambda (n) (A192490 (+ n n 1))))) ;; Requires _Antti Karttunen_'s IntSeq-library,
%Y A266409 Complement: A266410.
%Y A266409 Cf. A003309, A192490.
%Y A266409 Cf. A266350 (least monotonic left inverse).
%Y A266409 Cf. permutations A266418, A266638.
%Y A266409 Cf. also A005097.
%K A266409 nonn
%O A266409 1,2
%A A266409 _Antti Karttunen_, Jan 28 2016