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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
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
Sequence in context: A318859 A318817 A122626 * A231213 A231338 A257272
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.)