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Search: id:A006307
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| A006307 |
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Number of ways writing 2^n as unordered sums of 2 primes.
(Formerly M0344)
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+0
4
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| 0, 0, 1, 1, 2, 2, 5, 3, 8, 11, 22, 25, 53, 76, 151, 244, 435, 749, 1314, 2367, 4239, 7471, 13705, 24928, 45746, 83467, 153850, 283746, 525236, 975685, 1817111, 3390038, 6341424, 11891654, 22336060, 42034097, 79287664, 149711134, 283277225, 536710100, 1018369893
(list; graph; listen)
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OFFSET
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0,5
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Bohman, Jan and Froberg, Carl-Erik; Numerical results on the Goldbach conjecture. Nordisk Tidskr. Informationsbehandling (BIT) 15 (1975), no. 3, 239-243.
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LINKS
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Index entries for sequences related to Goldbach conjecture
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EXAMPLE
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n = 5: 2^5 = 32 = 3+29 = 13+19 so a(5) = 2.
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MAPLE
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a:=proc(n) local c, k; c:=0: for k from 1 to floor((n-1)/2) do if isprime(2*k+1)=true and isprime(2*n-2*k-1)=true then c:=c+1 else c:=c fi od end: 0, 0, 1, seq(a(2*2^n), n=1..15); (Deutsch)
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CROSSREFS
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a(n) = A061358(2^n). Cf. A062602, A062610.
Sequence in context: A045893 A071939 A075545 this_sequence A152991 A163298 A133440
Adjacent sequences: A006304 A006305 A006306 this_sequence A006308 A006309 A006310
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from David W. Wilson (davidwwilson(AT)comcast.net)
a(28)-a(35) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 21 2004
a(36)=79287664 and a(37)=149711134 from Ray Chandler (rayjchandler(AT)sbcglobal.net), Apr 10 2005
a(38)-a(40) from Russ Cox, Nov 04 2006
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