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A135025
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Let b(1) = 2; and for n>= 2, if b(n-1) < prime(n) then b(n) = b(n-1) + prime(n) otherwise b(n) = b(n-1) - prime(n). The sequence gives the indices n where b(n-1) < b(n) < b(n+1).
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5
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4, 9, 22, 57, 146, 367, 946, 2507, 6634, 17777, 48522, 133107, 369020, 1028405, 2880288, 8100949, 22877146, 64823569, 184274932, 525282741, 1501215194, 4299836187, 12340952050, 35486796313, 102220582466, 294917666855, 852123981582, 2465458792769
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OFFSET
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1,1
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COMMENTS
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The b sequence, prefixed by 0, is A008348. The low points in b are 1 less than the terms of the present sequence, and are given in A309226. - N. J. A. Sloane, Aug 31 2019
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LINKS
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EXAMPLE
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b(1) = 2
b(2) = 5
b(3) = 0
b(4) = 7
b(5) = 18
b(3) < b(4) < b(5), so 4 is the first term of the sequence.
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MAPLE
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B := proc(n) option remember ; if n = 1 then 2; else if procname(n-1)-ithprime(n) < 0 then procname(n-1)+ithprime(n) ; else procname(n-1)-ithprime(n) ; fi; fi; end: A135025 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if B(a-1) < B(a) and B(a) < B(a+1) then RETURN(a) ; fi; od: fi; end: for n from 1 do printf("%d, \n", A135025(n)) ; od: # R. J. Mathar, Feb 06 2009
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MATHEMATICA
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B[n_] := B[n] = If[n == 1, 2, If[B[n-1] - Prime[n] < 0, B[n-1] + Prime[n], B[n-1] - Prime[n]]];
a[n_] := a[n] = If[n == 1, 4, For[k = a[n-1]+1, True, k++, If[B[k-1] < B[k] && B[k] < B[k+1], Return[k]]]];
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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Lior Deutsch (liorde(AT)gmail.com), Feb 10 2008
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EXTENSIONS
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New term added by Lior Deutsch (liorde(AT)gmail.com), Oct 17 2008
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STATUS
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approved
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