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Numbers k such that k through k+6 all have the same number of divisors.
6

%I #40 Apr 11 2024 04:05:02

%S 171893,180965,647381,1039493,1071829,1450261,1563653,1713413,2129029,

%T 2384101,4704581,4773301,5440853,5775365,6627061,6644405,6697253,

%U 8556661,8833429,10531253,12101509,12238453,12307141,13416661,13970405

%N Numbers k such that k through k+6 all have the same number of divisors.

%C Allan Swett found that the first term not congruent to 5 mod 16 is 67073285. - _Ralf Stephan_, Nov 15 2004

%C Since A119479(n) < 7 for n < 8, no term has fewer than 8 divisors; the first that has more is a(30)=17476613. - _Ivan Neretin_, Feb 05 2016

%H Amiram Eldar, <a href="/A049053/b049053.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Donovan Johnson)

%H Jean-Marie De Koninck, Those Fascinating Numbers, Amer. Math. Soc., 2009, page 244.

%o (PARI) isok(n) = {my(nb = numdiv(n)); for (k=1, 6, if (numdiv(n+k) != nb, return (0));); 1;} \\ _Michel Marcus_, Feb 06 2016

%Y Cf. A000005, A006558, A019273, A119479.

%Y Other runs of equidivisor numbers: A005237 (runs of 2), A005238 (runs of 3), A006601 (runs of 4), A049051 (runs of 5), A049052 (runs of 6).

%K nonn

%O 1,1

%A _David W. Wilson_