A002329 -id:A002329 - cp's OEIS frontend

A170945 Least number k such that the decimal representation of 1/k has period Fibonacci(n).

3, 11, 27, 41, 73, 53, 43, 103, 1321, 497867, 323, 467, 11311, 20141, 12169, 232159532264041847249

Offset: 2

Michel Lagneau, Feb 19 2010

The period of 1/k is the least integer p such that 10^p = 1 (mod k). The integer p is also known as the multiplicative order of 10 (mod k).

			p(k) is the period of 1/k, we obtain with k=3,11,27,41,73,53,43,103 p(3)=1,p(11)=2,p(27)=3,p(41)=5,p(73)=8, p(53)=13,p(43)=21, p(103)=34

Mohammad K. Azarian, The Generating Function for the Fibonacci Sequence, Missouri Journal of Mathematical Sciences, Vol. 2, No. 2, Spring 1990, pp. 78-79. Zentralblatt MATH, Zbl 1097.11516.
Thomas Koshy, "Fibonacci and Lucas Numbers with Applications", John Wiley and Sons, 2001.
S. Vajda, Fibonacci and Lucas numbers and the Golden Section, Ellis Horwood Ltd., Chichester, 1989.

Dario Alejandro Alpern, Factorization using the Elliptic Curve Method
C. K. Caldwell, Fibonacci Numbers

Cf. A000045, A039834 (signed Fibonacci numbers), A002329, A072859 (periodic sequences), A003060

For the great numbers (p > 70), the maple program is very slow. That's what we use an process of two steps: factoring 10^p-1 with elliptic curve method (see the first web site), and then, for each factor q(k), k=1,2,...,r computation the periods of 1/q(k) and keep the period q(i) such that q(i) = Fibonacci number. The 17th term required 3h 2m for the computing of (10^1597) -1 T:=array(0..100);U:=array(0..100); n0:=0:n1:=1:T[1] = 1:for i from 2 to 30 do: n2:=n0+n1:T[i]:=n2:n0:=n1:n1:=n2:od:U[1]:=3:U[2]:=3:for q from 3 to 10 do: p0:=T[q]: indic:=0:for n from 1 to 2000 do:for p from 1 to 150 while(irem(10^p,n)<>1 or gcd(n,10)<>1 ) do:od: if irem(10^p,n) = 1 and gcd(n,10) = 1 and p=p0 and indic=0 then U[q]:=n:indic:=1:else fi:od: od: for n from 1 to 10 do:print( U[n]):od:

Edited by T. D. Noe, Apr 14 2010

A173394 Positions of powers of 2 in A084680.

Original entry on oeis.org

1, 3, 9, 11, 17, 33, 51, 73, 99, 101, 137, 153, 187, 219, 257, 303, 353, 411, 449, 561, 641, 657, 771, 803, 909, 1059, 1111, 1233, 1241, 1347, 1409, 1507, 1683, 1717, 1923, 2313, 2329, 2409, 2827, 3177, 3333, 3723, 3883, 4041, 4227, 4369, 4521, 4939

Offset: 1

Michel Lagneau, Feb 17 2010

nonn

The n where the decimal expansion of 1/n has a period length which is a power of 2.

			Period of 1/3 = 1. Period of 1/9 = 2. Period of 1/73 = 8. Period of 1/353 = 32.

J. W. L. Glaisher, On circulating decimals, Proc. Camb. Phil. Soc., 3 (1878), 185-206.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, pp. 7-12.

Eric Weisstein's World of Mathematics, Decimal Expansion.

Cf. A002329.

A084680 := proc(n) if gcd(n,10) <> 1 then 0 ; elif n = 1 then 1 ; else numtheory[order](10,n) ; end if; end proc:
isA000079 := proc(n) if n = 1 then true; elif n >=1 then numtheory[factorset](n) = {2} ; else false; end if; end proc:
for n from 1 to 5000 do if isA000079(A084680(n)) then printf("%d,",n) ; end if; end do: # R. J. Mathar, Mar 10 2010

{n: A084680(n) in A000079}.

Missing numbers -those where A084680(n)>1000- inserted - R. J. Mathar, Mar 10 2010

A179192 Numbers n, not relatively prime to 10, such that the decimal form of the period of 1/n is prime.

Original entry on oeis.org

12, 18, 30, 36, 45, 48, 75, 120, 180, 192, 198, 270, 288, 300, 330, 360, 450, 480, 495, 750, 768, 1152, 1200, 1584, 1800, 1875, 1920, 1980, 1998, 2304, 2700, 2880, 3000, 3072, 3300, 3330, 3600, 3690, 4500, 4800, 4950, 4995, 5625, 7500, 7680, 9090, 11520, 12000, 12288, 15840, 18000, 18432, 18750, 19200, 19800, 19980, 19998

Offset: 1

Michel Lagneau, Jul 01 2010

The sequence A175545 (numbers n such that the decimal form of the period of 1/n is prime) is only concerned with numbers n such that gcd(n,10)=1. Each number n such that gcd(n,10)<>1 generates a quotient where there exist a sequence of digits which is periodic after a finite sequence of digits, for example 1/36 = .0277777.... and 7 is periodic.
The prime numbers corresponding to this sequence are :
3, 5, 3, 7, 2, 3, 3, 3, 5, 3, 5, 37, 2, 3, 3, 7, 2, 3, 2,...

			1584 is in the sequence because 1/1584 = .0006313131313131313131... and 31 is prime.

H. Rademacher and O. Toeplitz, Von Zahlen und Figuren (Springer 1930, reprinted 1968), ch. 19, 'Die periodischen Dezimalbrueche'.

Cf. A175557, A175555, A178505, A045572, A002329

Reap[Do[p=RealDigits[1/n][[1,-1]]; If[GCD[10,n]>1 && Head[p] === List, While[p[[-1]] == 0, p=Most[p]]; If[PrimeQ[FromDigits[p]], Sow[n]]], {n, 20000}]][[2,1]]

Union of A179192 and A175545 is A061564.

Sequence corrected by T. D. Noe, Nov 18 2010

A235589 The periodic part of the decimal expansion of m/(m+1), for those m/(m+1) that have pure periods.

Original entry on oeis.org

6, 857142, 8, 90, 923076, 9411764705882352, 947368421052631578, 952380, 9565217391304347826086, 962, 9655172413793103448275862068, 967741935483870, 96, 972, 974358, 97560, 976744186046511627906, 9787234042553191489361702127659574468085106382, 979591836734693877551020408163265306122448

Offset: 1

Bill McEachen, Jan 12 2014

A companion sequence stemming from the some of the elements excluded by A156703. The sequence is highly volatile and infinite...as with A156703 the subset elements are encountered in numerical order. a(n) will start with the digit 9 for n>4 I believe. Entries can grow quite large very quickly. Each entry will be encountered once, and they will end in an even digit.

The number of digits of a(n) is given by A002329. - Michel Marcus, Aug 19 2015

			1/2=0.5 non-repeating, so exclude from sequence.
2/3=0.6 repeating, so a(1)=6.
5/6=0.833 (repeating) but has "8" prefix ahead of repeating "3" so exclude from sequence (decimal expansion not purely periodic)
6/7=0.857142 repeating so a(2)=857142.

Subsequence of A259299.

Cf. A156703, A036275, A060283, A114205.

FromDigits@ Flatten@ First@ RealDigits[(# - 1)/#] & /@ Select[Range@ 120, CoprimeQ[#, 10] &] //Rest (* Michael De Vlieger, Aug 18 2015 *)

a(n) = the periodic part of the decimal expansion of (A045572(n+1)-1) / A045572(n+1). - Doug Bell, Aug 17 2015

Missing terms added by Ralf Stephan, Jan 19 2014

Incorrect terms 916, 94 removed and two more terms added by Michael De Vlieger, Aug 18 2015

A173140 Numbers n such that the period of the decimal representation of 1/n is a square.

Original entry on oeis.org

3, 9, 17, 51, 81, 101, 153, 163, 187, 257, 303, 323, 489, 561, 577, 729, 771, 883, 909, 969, 1111, 1241, 1297, 1377, 1467, 1683, 1717, 1731, 1801, 1919, 2261, 2313, 2329, 2649, 2771, 2827, 2907, 2997, 3137, 3333, 3349, 3529, 3553, 3667, 3723, 3891, 4039, 4199, 4267, 4369, 4401, 4883

Offset: 1

Michel Lagneau, Feb 10 2010

The period p of 1/n is given by the smallest integer p for which 10^p == 1 (mod n). The periods of unit fractions are given by sequence A002329.

			period of 1/3 = 1;
period of 1/9 = 1;
period of 1/17 = 16;
period of 1/51 = 16.

J. W. L. Glaisher, On circulating decimals, Proc. Camb. Phil. Soc., 3 (1878), 185-206.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, pp. 7-12.

Eric Weisstein's World of Mathematics, Decimal Expansion
Eric Weisstein's World of Mathematics, Multiplicative Order

with(numtheory):n0:=60: ii:=1:tabl:=array(1..n0+1): for n from 2 to 10000 do: for p from 1 to 10000 while(irem(10^p,n)<>1 or gcd(n,10)<> 1) do: od: if irem(10^p,n) = 1 and gcd(n,10) = 1 and sqrt(p) = floor(sqrt(p)) then tabl[ii]:=n:ii:=ii+1:else fi:od: print(tabl):

Title rephrased, more terms and Maple program added; corrected by T. D. Noe and edited by Michel Lagneau, Apr 26 2010

A173491 a(n) is the least k such that the period of the decimal expansion of 1/k is A000204(n).

Original entry on oeis.org

3, 27, 101, 239, 21649, 19, 3191, 35121409, 722817036322379041, 2241, 797, 967, 1230610745978027, 3373, 60787, 509538919, 15060275578609, 5779, 37397, 423557

Offset: 1

Michel Lagneau, Feb 19 2010

Smallest k such that A007732(k) = A000204(n).

For the large numbers (p > 70), the Maple program below is very slow. So we use a process of two steps: first, factor 10^p-1 using the elliptic curve method; then, for each factor q(k), k=1,2,...,r, compute the period of 1/q(k) and keep the period q(i) such that q(i) ... [unfinished sentence? - R. J. Mathar, Feb 24 2010] Compare the Maple section of A170945!

			a(1)=3 because the period of 1/3 = 0.333... is 1, and 3 is the smallest number with that period.
a(2)=27 because the period of 1/27 = 0.037037... is 3 = A000204(2), and 27 is the smallest number with that period.
a(3)=101 because the period of 1/101 = 0.00990099... is 4 = A000204(3), and 101 is the smallest number with that period.
a(4)= 239 because the period of 1/239 = 0.00418410041841... is 7 = A000204(4), and 239 is the smallest number with that period.

V. E. Hoggatt, Jr., Fibonacci and Lucas Numbers. Houghton, Boston, MA, 1969.
Thomas Koshy, "Fibonacci and Lucas Numbers with Applications", John Wiley and Sons, 2001.
S. Vajda, Fibonacci and Lucas numbers and the Golden Section, Ellis Horwood Ltd., Chichester, 1989.

R. Javonovic, Lucas Function Calculator

Cf. A000032, A000204, A002329, A007732, A051626, A064362, A072859, A170945.

T:=array(0..100); U:=array(0..100); n0:=1: n1:=3: T[1] := 1: T[2] := 3:for i from 3 to 30 do: n2:=n0+n1: T[i]:=n2: n0:=n1: n1:=n2: od:
for q from 1 to 7 do: p0:=T[q]: indic:=0: for n from 1 to 25000 do: for p from 1 to 30 while(irem(10^p, n)<>1 or gcd(n,10)<>1 ) do: od: if irem(10^p,n) = 1 and gcd(n,10) = 1 and p=p0 and indic=0 then U[q]:=n: indic:=1: else fi: od: od:
for n from 1 to 7 do: print( U[n]): od:

(* This [slow] mma program gives all denominators < 50000 and disagrees with existing sequence for n = 11: a(11) = 797 instead of 29453 *) a204[n_] := a204[n] = Coefficient[Series[(2 - t )/(1 - t - t^2), {t, 0, n}], t^n] ; a7732[n_] := a7732[n] = MultiplicativeOrder[10, FixedPoint[Quotient[#, GCD[#, 10]] &, n]]; a[n_] := (k = 2; While[k++; k < 50000 && a7732[k] != a204[n] ]; k); Table[a[n], {n, 1, 15}](* Jean-François Alcover, Sep 02 2011 *)

References to unrelated sequences removed by R. J. Mathar, Feb 24 2010

Extended with the help of Jean-François Alcover and D. S. McNeil by T. D. Noe, Sep 07 2011

A175551 Decimal form of the period of 1/Fibonacci(n) for n such that gcd(10,Fibonacci(n)) = 1.

Original entry on oeis.org

3, 76923, 47619, 1123595505617977528089887640449438202247191

Offset: 1

Michel Lagneau, Jun 26 2010

A curiosity: the first six digits (with the first digit zero) of the 4th number, {0,1,1,2,3,5}, are the first six Fibonacci numbers!

The next number of this sequence contains 230 digits (decimal form of the period of 1/233 = 0.004291845493562231759656652360515021459227...).

			3 is in the sequence because Fibonacci(4) = 3 and 1/3 = 0.3333 => 3;
76923 is in the sequence because Fibonacci(7) = 13, and 1/13 = 0.076923 076923 => 76923.

Cf. A000045, A175545, A178505, A045572, A002329.

with(combinat, fibonacci):Digits:=100:nn:=10000:for m from 1 to nn do:n:=fibonacci(m):l:=length(n):z:=evalf(1/n): indic:=0:for p from 1 to nn do:if irem(10^p, n) = 1 and gcd(n, 5) = 1 and indic=0 then pp:=p:indic:=1:z1:=floor(z*10^pp): else fi:od:if indic=1 then printf(`%d, `, z1):else fi:od:

Name corrected by T. D. Noe, Jul 06 2010

A178495 Numbers k whose sum of digits equals the period of 1/k.

Original entry on oeis.org

1, 11, 41, 81, 111, 187, 231, 451, 567, 891, 1111, 1197, 1221, 1539, 1717, 1881, 2329, 2877, 3003, 3591, 3813, 4551, 4773, 5643, 6237, 6327, 7371, 8991, 9399, 9449, 10773, 11111, 11583, 13167, 13651, 15561, 16863, 17589, 23331, 24453, 27371, 39501

Offset: 1

Michel Lagneau, May 28 2010

			11 is in the sequence because 1 + 1 = 2 and 1/11 = 0.09 09 09... with period 2.
41 is in the sequence because 4 + 1 = 5 and 1/41 = 0.02439 02439 ... with period 5.

J. W. L. Glaisher, On circulating decimals, Proc. Camb. Phil. Soc., 3 (1878), pp. 185-206.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, pp. 7-12.

Eric Weisstein's World of Mathematics, Decimal Expansion.

Cf. A002329, A007953, A084680.

with(numtheory): nn:= 2343: T:=array(1..nn): U:=array(1..nn): X:=array(1..nn): Y:=array(1..nn):k:=1:for n from 2 to 999999 do:for p from 1 to 55 while(irem(10^p,n)<>1 or gcd(n,10)<> 1) do: od: if irem(10^p,n) = 1 and gcd(n,10) = 1 then T[k]:=n : U[k]:=p: k:=k+1:else fi:od: for n from 1 to nn do:p1:= T[n]: l:=length(p1):n0:=p1:s:=0:for m from 1 to l do:q:=n0:u:=irem(q,10):v:=iquo(q,10):n0:=v :s:=s+u:od: X[n]:=s: od: for n from 1 to nn do:if X[n]= U[n] then printf(`%d, `, T[n]):else fi:od:

{k: A084680(k) = A007953(k)}. - R. J. Mathar, Jun 07 2010

A178836 Numbers n such that the period of 1/n equals the period of 1/R(n), where R(n) (A004086) is the reversal of n.

Original entry on oeis.org

3, 7, 9, 11, 33, 77, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 303, 313, 323, 333, 343, 353, 363, 373, 383, 393, 707, 717, 727, 737, 747, 757, 767, 777, 787, 797, 909, 919, 929, 939, 949, 959, 969, 979, 989, 999, 1001, 1111, 1221, 1331, 1441, 1551

Offset: 1

Michel Lagneau, Jun 16 2010

Non-palindromic numbers are included in this sequence :

{3267, 3927, 7293, 7632,...}

			3267 is in the sequence because period (1/3267) = 66 and also period(1/7623) = 66.
3927 is in the sequence because period (1/3927) = 48 and also period(1/7293) = 48.

Cf. A004086, A045572, A002329.

with(numtheory): nn:=8000:for n from 3 to nn do: s:=0:l:=length(n):for q from 0 to l-1 do:x:=iquo(n,10^q):y:=irem(x,10):s:=s+y*10^(l-1-q): od: indic1:=0:for p from 1 to nn do:if irem(10^p, n) = 1 and gcd(n, 5) = 1 and indic1=0 then pp:=p: indic1:=1:else fi:od: indic2:=0:for p from 1 to nn do:if irem(10^p, s) = 1 and gcd(s, 5) = 1 and indic2=0 then ppp:=p:indic2:=1:else fi:od: if pp=ppp and indic1=1 and indic2=1 then print(n):else fi:od:

A279535 Triangle read by rows: The number of digits in the smallest 9-repdigit that is a multiple of n and m, where n and m are coprime to 2 and 5.

Original entry on oeis.org

1, 1, 1, 6, 6, 42, 1, 3, 6, 9, 2, 2, 6, 2, 22, 6, 6, 6, 6, 6, 78, 16, 16, 48, 16, 16, 48, 272, 18, 18, 18, 18, 18, 18, 144, 342, 6, 6, 42, 6, 6, 6, 48, 18, 42, 22, 22, 66, 22, 22, 66, 176, 198, 66, 506, 3, 9, 6, 27, 6, 6, 48, 18, 18, 66, 81, 28, 28, 84, 28, 28, 84, 112, 252, 84, 308, 84, 812

Offset: 1

R. J. Mathar, Dec 14 2016

The number of digits of the smallest member of A002283 divisible by n and m, as n and m run through A045572. Numbers of the form 10^d-1 are not divisible through 5 or 2, so these are excluded in the table. Losely related to A278588.

			The 3rd smallest number coprime to 2 and 5 is A045572(3)=7. The smallest 9-repdigit divisible by 7*7=49 is 10^42-1 = A002283(42), to T(3,3)=42.
The triangle starts
   1;
   1,  1;
   6,  6, 42;
   1,  3,  6,  9;
   2,  2,  6,  2, 22;
   6,  6,  6,  6,  6, 78;
  16, 16, 48, 16, 16, 48, 272;

Cf. A002283, A002329, A045572

T(i,j) = min{d: (n*m) | (10^d-1)} where n=A045572(i) and m=A045572(j).

cp's OEIS Frontend

A170945 Least number k such that the decimal representation of 1/k has period Fibonacci(n).

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A173394 Positions of powers of 2 in A084680.

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A179192 Numbers n, not relatively prime to 10, such that the decimal form of the period of 1/n is prime.

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A235589 The periodic part of the decimal expansion of m/(m+1), for those m/(m+1) that have pure periods.

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A173140 Numbers n such that the period of the decimal representation of 1/n is a square.

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A173491 a(n) is the least k such that the period of the decimal expansion of 1/k is A000204(n).

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A175551 Decimal form of the period of 1/Fibonacci(n) for n such that gcd(10,Fibonacci(n)) = 1.

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