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 A135025 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). 5
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 LINKS Table of n, a(n) for n=1..28. EXAMPLE 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. MAPLE 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 MATHEMATICA 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]]]]; Table[Print[n, " ", a[n]]; a[n], {n, 1, 16}] (* Jean-François Alcover, Aug 16 2022, after R. J. Mathar *) CROSSREFS Cf. A008348, A135026, A309226. Sequence in context: A318859 A318817 A122626 * A231213 A231338 A257272 Adjacent sequences: A135022 A135023 A135024 * A135026 A135027 A135028 KEYWORD nonn,more AUTHOR Lior Deutsch (liorde(AT)gmail.com), Feb 10 2008 EXTENSIONS New term added by Lior Deutsch (liorde(AT)gmail.com), Oct 17 2008 Definition corrected and entry revised by Robert Israel, Michel Marcus, and N. J. A. Sloane, Sep 29 2014 a(17)-a(28) from Giovanni Resta, Oct 02 2019 STATUS approved

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Last modified March 4 02:53 EST 2024. Contains 370522 sequences. (Running on oeis4.)