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 A261067 a(n) = (11^(2^n) - 1)/2^(n + 2). 1

%I

%S 15,915,6698715,717964529118315,16495138082306681918325119173515,

%T 17413733142679306233865281770975943513633443105435651232476307915

%N a(n) = (11^(2^n) - 1)/2^(n + 2).

%C (m^(2^n) - 1)/2^(n + 2) is an integer for any odd value of m and n > 0.

%C In particular, for m = 11, a(n) is a multiple of 15.

%F a(n) = 15*A068533(n). - _Michel Marcus_, Aug 14 2015

%e a(3) = (11^8 - 1)/2^5 = 6698715.

%p A261067:=n->(11^(2^n) - 1)/2^(n + 2): seq(A261067(n), n=1..8); # _Wesley Ivan Hurt_, Jan 27 2017

%t Table[(11^(2^n) - 1)/2^(n + 2), {n, 10}] (* _Vincenzo Librandi_, Aug 14 2015 *)

%o (PARI) first(m)=vector(m,i, (11^(2^i)-1)/2^(i+2)); /* _Anders HellstrĂ¶m_, Aug 08 2015 */

%o (MAGMA) [(11^(2^n)-1)/2^(n+2): n in [1..6]]; // _Vincenzo Librandi_, Aug 14 2015

%Y Cf. A059723, A068531, A068533, A097421.

%K nonn,easy

%O 1,1

%A _Marco RipĂ _, Aug 08 2015

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Last modified April 3 04:21 EDT 2020. Contains 333195 sequences. (Running on oeis4.)