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A251393 Indices of powers of 2 in A098550.

%I A251393 #23 Jan 27 2025 22:52:06
%S A251393 1,2,4,6,14,29,65,137,277,546,1109,2208,4391,8746,17404,34662,69036,
%T A251393 137604,274385,547278,1091962,2179171,4349905,8684545,17341369,
%U A251393 34632301,69172557,138175535,276039015,551501773
%N A251393 Indices of powers of 2 in A098550.
%H A251393 Rémy Sigrist, <a href="/A251393/a251393.txt">C program</a>
%F A251393 A098550(a(n)) = 2^(n-1).
%F A251393 A209229(A098550(a(n))) = 1.
%o A251393 (Haskell)
%o A251393 a251393 n = a251393_list !! (n-1)
%o A251393 a251393_list = filter ((== 1) . a209229 . a098550) [1..]
%o A251393 (Python)
%o A251393 from math import gcd
%o A251393 A251393_list, l1, l2, s, p2, b = [1,2], 3, 2, 4, 4, {}
%o A251393 for n in range(4,10**4):
%o A251393     i = s
%o A251393     while True:
%o A251393         if not i in b and gcd(i,l1) == 1 and gcd(i,l2) > 1:
%o A251393             l2, l1, b[i] = l1, i, 1
%o A251393             while s in b:
%o A251393                 b.pop(s)
%o A251393                 s += 1
%o A251393             if i == p2:
%o A251393                 A251393_list.append(n)
%o A251393                 p2 *= 2
%o A251393             break
%o A251393         i += 1 # _Chai Wah Wu_, Dec 03 2014
%o A251393 (C) // See Links section.
%Y A251393 Subsequence of A251241.
%Y A251393 Cf. A098550, A209229, A251394.
%K A251393 nonn,more
%O A251393 1,2
%A A251393 _Reinhard Zumkeller_, Dec 03 2014
%E A251393 a(18)-a(19) from _Chai Wah Wu_, Dec 03 2014
%E A251393 a(20) from _Chai Wah Wu_, Dec 04 2014
%E A251393 a(21)-a(22) from _Rémy Sigrist_, Nov 08 2022
%E A251393 a(23)-a(30) from _Jinyuan Wang_, Jan 27 2025