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Indices n of odd numbers 2n+1 such that k + 2^m is prime, where k and m are the odd part and 2-valuation, respectively, of 2n.
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%I #16 Jan 02 2023 12:30:54

%S 1,2,3,5,6,8,9,11,12,14,15,17,18,20,21,24,26,27,29,30,35,36,38,39,41,

%T 44,45,50,51,54,56,57,59,60,65,66,69,71,74,77,78,80,81,84,86,87,92,95,

%U 96,98,99,101,104,105,107,110,111,114,116,120,125,126,128,129,132,134

%N Indices n of odd numbers 2n+1 such that k + 2^m is prime, where k and m are the odd part and 2-valuation, respectively, of 2n.

%C It appears that about 1/log_10(N) of the odd numbers below 2N have this property: for n < 10^k with k = (1, 2, 3, 4, 5, 6), there are (7, 51, 364, 2675, 20668, 167185) numbers as defined in NAME.

%C See the sequence A332075 of the corresponding odd numbers for more information.

%H T. Ordowski, <a href="http://list.seqfan.eu/oldermail/seqfan/2020-August/020922.html">Problem</a>, post to the SeqFan list, Aug. 11, 2020

%t Select[Range[134], PrimeQ[(m = 2^IntegerExponent[2*#, 2]) + 2*#/m] &] (* _Amiram Eldar_, Aug 16 2020 *)

%o (PARI) select( {is_A332076(n)=ispseudoprime((n>>n=valuation(n,2))+2<<n)}, [1..199])

%Y Cf. A000040 (primes), A000265 (odd part), A007814 (2-valuation), A332075 (the corresponding odd numbers).

%K nonn

%O 1,2

%A _M. F. Hasler_, Aug 13 2020