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Numbers m such that A007947(m) = A007947(k) and A007947(m+1) = A007947(k+1), for some k < m.
3

%I #16 Apr 18 2021 06:05:35

%S 8,48,224,960,1215,3968,16128,65024,261120,1046528,4190208,16769024,

%T 67092480,268402688,1073676288,4294836224

%N Numbers m such that A007947(m) = A007947(k) and A007947(m+1) = A007947(k+1), for some k < m.

%C For every k > 1, the sequence includes 4^k - 2^(k+1), with m = 2^k - 2. - _David Wasserman_, Jan 29 2004

%C a(12) <= 16769024. a(13) <= 67092480. a(14) <= 268402688. a(15) <= 1073676288. [_Donovan Johnson_, Dec 19 2008]

%e A007947(8) = A007947(2) and A007947(9) = A007947(3), so 8 is in the sequence.

%o (PARI) rad(n) = factorback(factorint(n)[, 1]); \\ A007947

%o isok(m) = {my(rm = rad(m), sm = rad(m+1)); for (k=1, m-1, if ((rad(k) == rm) && (rad(k+1) == sm), return (1)););} \\ _Michel Marcus_, Apr 05 2021

%Y Cf. A007947, A088966.

%K nonn,hard,more

%O 1,1

%A _Naohiro Nomoto_, Oct 26 2003

%E a(7)-a(11) from _Donovan Johnson_, Dec 19 2008

%E Name edited by _Michel Marcus_, Apr 06 2021

%E Confirmed a(12)-a(15) and extended with a(16) by _Martin Ehrenstein_, Apr 18 2021