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 A081468 a(n) is the smallest multiple of n of the type k*n + k*(k+1)/2, i.e., the smallest sum (n+1) to (n+k) which is divisible by n. 6
 2, 12, 9, 56, 30, 24, 63, 240, 108, 50, 165, 132, 234, 126, 90, 992, 408, 180, 513, 420, 147, 308, 759, 480, 900, 390, 1053, 224, 1218, 570, 1395, 4032, 429, 680, 595, 324, 1998, 912, 546, 720, 2460, 1050, 2709, 1936, 450, 1334, 3243, 2064, 3528, 1500, 1020 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From Robert Israel, Jun 26 2018: (Start) a(n) = 3*n*(n-1)/2 if n is an odd prime power. a(2^k) = 4^(k+1) - 2^(k+1). (End) LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(4) = 5 + 6 + 7 + 8 + 9 + 10 + 11 = 56; A081467(4) = 11. MAPLE f:= proc(n) local k; k:= min(map(t ->rhs(op(t)), {msolve(k*(k+1), 2*n)}) minus {0}); k*n+k*(k+1)/2 end proc: f(1):= 2: map(f, [\$1..100]); # Robert Israel, Jun 26 2018 MATHEMATICA a[n_] := For[k = 1, True, k++, If[Divisible[m = k n + k(k+1)/2, n], Return[m] ] ]; Array[a, 100] (* Jean-François Alcover, Mar 25 2019 *) PROG (PARI) a(n) = {my(k = 1); while((s=k*n + k*(k+1)/2) % n, k++); s; } \\ Michel Marcus, Jul 29 2017 CROSSREFS Cf. A081467, A081469, A081470, A081471, A081472. Sequence in context: A002209 A100654 A166544 * A216349 A280015 A343645 Adjacent sequences: A081465 A081466 A081467 * A081469 A081470 A081471 KEYWORD nonn,look AUTHOR Amarnath Murthy, Mar 23 2003 EXTENSIONS More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 06 2003 STATUS approved

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Last modified November 29 19:34 EST 2023. Contains 367447 sequences. (Running on oeis4.)