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%I #25 Nov 10 2020 04:20:28
%S 45,76,99,117,148,172,243,244,245,333,388,508,549,604,605,725,845,909,
%T 932,964,1076,1084,1252,1325,1413,1468,1557,1588,1676,1773,2524,2525,
%U 2637,2645,2764,3284,3357,3412,3509,3789,3988,4076,4204,4205,4419,4492,4805,4869,4924,4925
%N Numbers k such that k and k-1 both have 6 divisors.
%D David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, 1986, p. 103.
%H Amiram Eldar, <a href="/A049104/b049104.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Vincenzo Librandi)
%F a(n) = A049103(n)+1. - _Zak Seidov_, Feb 11 2016
%t Flatten[Position[Partition[Table[DivisorSigma[0, n-1], {n, 5000}], 2, 1], _?(#=={6, 6} &)]] (* _Vincenzo Librandi_, Oct 21 2012 *)
%o (PARI) isok(n) = (numdiv(n) == 6) && (numdiv(n-1) == 6); \\ _Michel Marcus_, Feb 11 2016
%Y Cf. A038400, A049103.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, _Felice Russo_, _Olivier Gérard_
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