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%I #15 Jul 08 2022 18:02:47
%S 2,1,3,2,1,3,1,5,4,2,1,7,6,5,4,2,7,5,3,1,5,2,1,3,9,7,4,2,1,11,13,10,8,
%T 6,1,11,7,4,11,3,17,14,13,9,8,6,5,4,2,11,19,18,17,14,12,11,10,9,7,4,2,
%U 1,17,9,7,3,16,10,5,4,1,21,15,13,10,5,4,1,13,9,2
%N The exponent k which defines A181741(n) = 2^t-2^k-1.
%F k = A007814(A181741(n)+1). [_R. J. Mathar_, Nov 18 2010]
%t IntegerExponent[Select[Table[2^t-2^k-1, {t, 1, 20}, {k, 1, t-1}] // Flatten // Union, PrimeQ] + 1, 2] (* _Amiram Eldar_, Dec 17 2018 after _Jean-François Alcover_ at A181741 *)
%o (PARI) listk(nn) = {for (n=3, nn, forstep(k=n-1, 1, -1, if (isprime(2^n-2^k-1), print1(k, ", "));););} \\ _Michel Marcus_, Dec 17 2018
%o (Python)
%o from itertools import count, islice
%o from sympy import isprime
%o def A181743_gen(): # generator of terms
%o m = 2
%o for t in count(1):
%o r=1<<t-1
%o for k in range(t-1,0,-1):
%o if isprime(m-r-1):
%o yield k
%o r>>=1
%o m<<=1
%o A181743_list=list(islice(A181743_gen(),30)) # _Chai Wah Wu_, Jul 08 2022
%Y Cf. A181741, A181742.
%K nonn
%O 1,1
%A _Vladimir Shevelev_, Nov 08 2010
%E Terms equivalent to insertions in A181741 inserted by _R. J. Mathar_, Nov 18 2010
%E More terms from _Michel Marcus_, Dec 17 2018
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