

A309203


Numbers k such that A111273(k1) = 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
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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



