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Numbers of the form 2^(m-1)*(4^m+2^m-1) where 4^m+2^m-1 is prime.
2

%I #7 Nov 07 2016 14:38:00

%S 5,38,284,2168,133088,537394688,140739635806208,

%T 2361183382172302573568,151115729703628426969088,

%U 20282409604241966234288777068544,45671926166590726335069952848216804538059849728

%N Numbers of the form 2^(m-1)*(4^m+2^m-1) where 4^m+2^m-1 is prime.

%C This sequence is a subsequence of A110079 namely, if n is in the sequence then sigma(n)=2n-2^d(n) where d(n) is number of positive divisors of n(see comments line of the sequence A110079). Sequence A110080 gives numbers n such that 4^n+2^n-1 is prime.

%H F. Firoozbakht, M. F. Hasler, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL13/Hasler/hasler2.html">Variations on Euclid's formula for Perfect Numbers</a>, JIS 13 (2010) #10.3.1

%e 2^1299*(4^1300+2^1300-1) is in the sequence because 4^1300+2^1300-1 is prime.

%t Do[If[PrimeQ[4^m+2^m-1], Print[2^(m-1)*(4^m+2^m-1)]], {m, 52}]

%Y Cf. A110079, A098855.

%K nonn

%O 1,1

%A _Farideh Firoozbakht_, Aug 03 2005