A127956 -id:A127956 - cp's OEIS frontend

A127965 Number of bits in A127962(n).

2, 4, 6, 10, 12, 16, 18, 22, 30, 42, 60, 78, 100, 126, 166, 190, 198, 312, 346, 700, 1708, 2616, 3538, 5806, 10500, 10690, 11278, 12390, 14478, 42736, 83338, 95368, 117238, 127030, 138936, 141078, 267016, 269986, 374320, 986190, 4031398

Offset: 1

Artur Jasinski, Feb 09 2007

Cf. A127962, A127963, A127964, A127961, A000979, A000978, A124400, A126614, A127955, A127956, A127957, A127958, A127936.

b = {}; Do[c = 1 + Sum[2^(2n - 1), {n, 1, x}]; If[PrimeQ[c], AppendTo[b, c]], {x, 0, 1000}]; a = {}; Do[AppendTo[a, FromDigits[IntegerDigits[b[[x]], 2]]], {x, 1, Length[b]}]; d = {}; Do[AppendTo[d, DigitCount[a[[x]], 10, 0]+DigitCount[a[[x]], 10, 1]], {x, 1, Length[a]}]; d

a(n) = A127964(n) + A127963(n).

a(n) = 1 + floor(log_2(A000979(n))) = 1 + floor(log_2(2^A000978(n)+1) - A020857) = A000978(n) - 1. - R. J. Mathar, Feb 01 2008

a(22)-a(29) from Vincenzo Librandi, Mar 30 2012

a(30)-a(41) from Amiram Eldar, Oct 19 2024

A127959 Nonprime numbers of the form 1 + Sum_{k=1..m} 2^(2*k - 1).

Original entry on oeis.org

171, 10923, 699051, 11184811, 44739243, 178956971, 2863311531, 11453246123, 45812984491, 183251937963, 733007751851, 11728124029611, 46912496118443, 187649984473771, 750599937895083, 3002399751580331, 12009599006321323

Offset: 1

Artur Jasinski, Feb 09 2007

nonn

Prime numbers of the form 1 + Sum_{k=1..m} 2^(2*n - 1) is A000979. Numbers x such that 1 + Sum_{k=1..m} 2^(2*n - 1) is prime for n=1,2,...,x is A127936. A127955 is probably a subset of the present sequence.

Cf. A000979, A000978, A124400, A126614, A127955, A127956, A127957, A127958, A127936.

a = {}; Do[c = 1 + Sum[2^(2n - 1), {n, 1, x}]; If[PrimeQ[c] == False, AppendTo[a, c]], {x, 1, 50}]; a
Select[Table[Sum[2^(2k-1),{k,n}]+1,{n,50}],!PrimeQ[#]&] (* Harvey P. Dale, Dec 23 2017 *)

cp's OEIS Frontend

A127965 Number of bits in A127962(n).

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