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 A309203 Numbers k such that A111273(k-1) = k. 2
 3, 5, 7, 11, 13, 17, 19, 23, 27, 29, 31, 35, 37, 39, 41, 43, 45, 47, 53, 55, 59, 61, 63, 67, 71, 73, 77, 79, 83, 89, 95, 97, 99, 101, 103, 107, 109, 113, 115, 119, 125, 127, 131, 135, 137, 139, 141, 147, 149, 151, 155, 157, 163, 167, 171, 173, 179, 181, 191, 193, 197, 199, 207, 211, 215, 219 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are odd; includes all odd primes. The odd terms that are not primes are 27, 35, 39, 45, 55, 63, 77, 95, 99, 115, 119, 125, 135, 141, 147, 155, 171, ....  What are these numbers? LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE S:= {}: R:= NULL: count:= 0: for n from 1 while count < 200 do   v:= min(numtheory:-divisors(n*(n+1)/2) minus S);   S:= S union {v};   if v = n+1 then R:= R, n+1; count:= count+1 fi; od: R; # Robert Israel, Jul 30 2019 CROSSREFS Cf. A111273. Sequence in context: A122089 A109860 A100392 * A176847 A067019 A132106 Adjacent sequences:  A309200 A309201 A309202 * A309204 A309205 A309206 KEYWORD nonn AUTHOR N. J. A. Sloane, Jul 27 2019 STATUS approved

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Last modified May 19 11:21 EDT 2022. Contains 353833 sequences. (Running on oeis4.)