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%I #42 Dec 09 2024 04:48:20
%S 3,5,47,53,1374,1386,3738,3756,6680,6704,84626,84658,89480,89522,
%T 91832,91880,173092,173152,192882,192950,524587,524661,865301,865385,
%U 876543,876641,890479,890583,904273,904383,918859,918987,1628979,1629117,1647107,1647257,1666775
%N Index of first occurrence of n-th prime in A307720.
%C It follows from the definition of A307720 that if p = k-th prime, k>1 and k odd, and q = (k+1)st prime, then the first time p appears in the sequence is at the start of a subsequence (p,1) [(p-1)/2 times], p, (1,q) [(q+1)/2 times].
%C For example, the fifth prime (11) first appears in A307720 at step 1374 at the start of the subsequence 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 11, 1, 13, 1, 13, 1, 13, 1, 13, 1, 13, 1, 13, 1, 13.
%C So q appears p+1 steps after p, which explains why the terms of the present sequence appear in pairs.
%C In fact, it appears that one can make a much stronger statement about what happens immediately after the first occurrence of p. Look at the terms in A307720 following the first 11 at step 1374. It may be that the next O(p^2) terms are forced.
%H N. J. A. Sloane, <a href="/A307632/b307632.txt">Table of n, a(n) for n = 1..1229</a> (taken from Rémy Sigrist's b-file for A307630; first 132 terms from Hans Havermann)
%Y Cf. A307720, A307630, A307631.
%Y First differences = A348773.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Apr 26 2019
%E More terms from _Hans Havermann_, Apr 26 2019