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 A066480 Start of first run of exactly n consecutive integers with same number of anti-divisors. 1
 5, 1, 19, 212, 231, 353755, 7077517, 841891, 96723128, 640141432, 83101215664, 3774913237385, 29738569261171 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS See A066272 for definition of anti-divisor. a(11) > 10^10. - Donovan Johnson, Apr 13 2013 LINKS Jon Perry, The Anti-Divisor Jon Perry, The Anti-divisor [Cached copy] Jon Perry, The Anti-divisor: Even More Anti-Divisors [Cached copy] EXAMPLE To illustrate the first 3 terms, here are the numbers of anti-divisors of the numbers 1 through 22: [0, 0, 1, 1, 2, 1, 3, 2, 2, 3, 3, 2, 4, 3, 3, 2, 5, 4, 3, 3, 3, 5] (see A066272). - N. J. A. Sloane, Oct 14 2019 MAPLE with(numtheory); A066480:=proc(q) local a, b, c, j, k, n, t, v; v:=array(1..1000); for j from 1 to 1000 do v[j]:=0; od; n:=1; a:=0; while n<=q do   b:=0; for k from 2 to n-1 do if abs((n mod k)-k/2)<1 then b:=b+1; fi; od;   t:=n; c:=b;  while c=b do t:=t+1;     b:=0; for k from 2 to t-1 do if abs((t mod k)-k/2)<1 then b:=b+1; fi; od; od;   if t-n=a+1 then a:=t-n; print(n); j:=1;    while v[a+j]>0 do a:=t-n+j; print(v[a]); j:=j+1; od;   else if t-n>a+1 then if v[t-n]=0 then v[t-n]:=n; fi; fi; fi;   n:=t; od; print(); end: A066480(10^9); # Paolo P. Lava, Apr 16 2013 MATHEMATICA a066272[n_] := Count[Range[2, n - 1], _?(Abs[Mod[n, #] - #/2] < 1 &)] a[0] = 5; a[n_] := For[i = 1, True, ++i, If[Equal @@ Table[a066272[j], {j, i, i + n}], Return[i]]] a /@ Range[0, 4] (* Julien Kluge, Dec 03 2016 *) PROG (PARI) nbad(n) = #select(t->n%t && t1) && nbad(k-1) == nb, return (0)); for (j=1, n-1, if (nbad(k+j) != nb, return(0)); ); nbad(k+n) != nb; } a(n) = my(k=1); while (!isok(k, n), k++); k; \\ Michel Marcus, Oct 11 2019 CROSSREFS Cf. A066272, A006558. Sequence in context: A286232 A147437 A147369 * A136394 A145372 A145373 Adjacent sequences:  A066477 A066478 A066479 * A066481 A066482 A066483 KEYWORD nonn,more AUTHOR Robert G. Wilson v, Jan 02 2002 EXTENSIONS a(7) corrected and a(9)-a(10) from Donovan Johnson, Apr 13 2013 a(11)-a(12) from Jud McCranie, Oct 10 2019 a(11)-a(12) decremented by 1 by Michel Marcus, Oct 17 2019 a(13) from Jud McCranie, Oct 22 2019 STATUS approved

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)