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%I #9 Oct 30 2021 01:25:16
%S 1,2,4,6,48,50,52,54,56,58,1375,1377,1379,1381,1383,1385,1387,1389,
%T 1391,1393,1395,1397,3739,3741,3743,3745,3747,3749,3751,3753,3755,
%U 3757,3759,3761,3763,3765,3767,3769,3771,3773,6681,6683,6685,6687,6689,6691,6693,6695,6697,6699,6701,6703,6705
%N Indices of 1's in A307720.
%C Theorem: This sequence is infinite. Proof: Every prime in A307720 is immediately preceded or followed by a 1. - _N. J. A. Sloane_, Oct 30 2021
%C The start of this sequence consists of arithmetic progressions of constant difference 2 and lengths 1, 3, 6, 12, 18, 26, 76, ... that start with 1, 2, 48, 1375, 3739, 6681, 84627, 91833, ... It would be nice to have an alternative way to explain these numbers.
%H N. J. A. Sloane, <a href="/A348244/b348244.txt">Table of n, a(n) for n = 1..927</a>
%Y Cf. A307720.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Oct 16 2021