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 A161570 Sum of all numbers from n up to A018252(n). 4
 1, 9, 18, 30, 35, 40, 57, 77, 84, 91, 116, 144, 153, 162, 195, 205, 215, 225, 235, 275, 318, 330, 342, 354, 366, 416, 429, 442, 497, 555, 570, 585, 648, 664, 680, 696, 712, 782, 799, 816, 833, 850, 927, 1007, 1026, 1045, 1064, 1083, 1170, 1190, 1210, 1302 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) = A000217(A018252(n)) - A000217(n-1). EXAMPLE a(2) = 2 + 3 + 4 = 9; a(3) = 3 + 4 + 5 + 6 = 18; a(4) = 4 + 5 + 6 + 7 + 8 = 30. MAPLE A018252 := proc(n) option remember ; if n = 1 then 1; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A000217 := proc(n) n*(n+1)/2 ; end: A161570 := proc(n) A000217( A018252(n)) - A000217(n-1) ; end: seq(A161570(n), n=1..90) ; # R. J. Mathar, Aug 03 2009 PROG (PARI) print1(n=1); p=3; forprime(q=5, 97, for(k=p+1, q-1, print1(", "k*(k+1)/2-n++*(n-1)/2)); p=q) \\ Charles R Greathouse IV, Sep 03 2011 CROSSREFS Cf. A018252, A000217. Sequence in context: A107223 A194152 A044433 * A140089 A183444 A221533 Adjacent sequences:  A161567 A161568 A161569 * A161571 A161572 A161573 KEYWORD nonn,easy AUTHOR Juri-Stepan Gerasimov, Jun 14 2009 EXTENSIONS a(26) corrected and extended by R. J. Mathar, Aug 03 2009 Definition rephrased by R. J. Mathar, Sep 11 2009 STATUS approved

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Last modified August 6 19:52 EDT 2020. Contains 336256 sequences. (Running on oeis4.)