Sequence A084250: a(2^n)=2^(n+1)-1?
Roland Bacher
Roland.Bacher at ujf-grenoble.fr
Thu May 22 09:06:36 CEST 2003
The second sequence A084251 is very close to the famous sequence
giving the number of partitions of integers
ID Number: A000041 (Formerly M0663 and N0244)
Sequence: 1,1,2,3,5,7,11,15,22,30,42,56,77,101,135,176,231,297,385,
490,627,792,1002,1255,1575,1958,2436,3010,3718,4565,5604,
6842,8349,10143,12310,14883,17977,21637,26015,31185,37338,
44583,53174,63261,75175,89134
Name: a(n) = number of partitions of n (the partition numbers).
is this a mere coincidence? Roland Bacher
> Consider the new sequences A084250 and A084251 given below.
>
> Observe that: a(2^n) = 2^(n+1) - 1 (at least for n<=64),
> although I can not guess why this should be true.
>
> Could someone give a rationale for this to be true (if so)?
>
> Also, I would appreciate it if someone could extend
> these sequences to test the a(2^n) conjecture.
>
> Thanks Much,
> Paul
> --------------------------------------------------------
> ID Number: A084250.
>
> Least distinct positive integers such that
>
> exp(sum(n>=1,a(n)*x^n/n))
>
> yields an integer power series (A084251), where a(1)=1.
>
>
> Conjecture: a(2^n) = 2^(n+1) - 1.
>
>
> A084250 is a permutation of the natural numbers:
>
> 1, 3, 4, 7, 6, 12, 8, 15, 13, 18,
> 23, 16, 14, 10, 9, 31, 35, 21, 20, 2,
> 11, 25, 24, 48, 56, 42, 40, 70, 30, 27,
> 32, 63, 26, 37, 83, 61, 38, 22, 17, 50,
> 124,19, 44, 29,108, 72, 95, 64, 57, 68,
> 89, 46,107,102,138, 78, 80, 90, 60, 71,
> 62, 34,146,127, 84,100,...
> --------------------------------------------------------
> ID Number: A084251.
>
> Integer sequence defined by
>
> exp(sum(n>=1,A084250(n)*x^n/n)) = sum(n>=0,A084251(n)*x^n)
>
> where A084250 is the least distinct positive integers
> such that A084251(n) is an integer for all n>=0.
>
> A084251 begins:
>
> 1,1,2,3,5,7,11,15,22,30,42,
> 57,77,102,135,176,230,297,381,486,616,
> 777,976,1219,1517,1880,2320,2854,3499,4273,5203,
> 6315,7645,9228,11111,13344,15987,19106,22786,27113,32197,
> 38158,45132,53283,62793,73871,86754,101718,119069,139170,162416,
> 189276,220261,255969,297062,344308,398558,460794,532099,613722,707054,
> 813671,935344,1074072,1232086,1411912,1616377,...
>
> Example.
>
> A(x) = exp(x + 3x^2/2 + 4x^3/3 + 7x^4/4 + 6x^5/5 + 12x^6/6 +...)
> = 1 + 1x + 2x^2 + 3x^3 + 5x^4 + 7x^5 + 11x^6 +...
> --------------------------------------------------------
>
> Table of the two sequences:
>
> n A084250 A084251
> -- ------- -------
> 0. _ 1
>
> 1. 1 1
>
> 2. 3 2
> 3. 4 3
>
> 4. 7 5
> 5. 6 7
> 6. 12 11
> 7. 8 15
>
> 8. 15 22
> 9. 13 30
> 10. 18 42
> 11. 23 57
> 12. 16 77
> 13. 14 102
> 14. 10 135
> 15. 9 176
>
> 16. 31 230
> 17. 35 297
> 18. 21 381
> 19. 20 486
> 20. 2 616
> 21. 11 777
> 22. 25 976
> 23. 24 1219
> 24. 48 1517
> 25. 56 1880
> 26. 42 2320
> 27. 40 2854
> 28. 70 3499
> 29. 30 4273
> 30. 27 5203
> 31. 32 6315
>
> 32. 63 7645
> 33. 26 9228
> 34. 37 11111
> 35. 83 13344
> 36. 61 15987
> 37. 38 19106
> 38. 22 22786
> 39. 17 27113
> 40. 50 32197
> 41. 124 38158
> 42. 19 45132
> 43. 44 53283
> 44. 29 62793
> 45. 108 73871
> 46. 72 86754
> 47. 95 101718
> 48. 64 119069
> 49. 57 139170
> 50. 68 162416
> 51. 89 189276
> 52. 46 220261
> 53. 107 255969
> 54. 102 297062
> 55. 138 344308
> 56. 78 398558
> 57. 80 460794
> 58. 90 532099
> 59. 60 613722
> 60. 71 707054
> 61. 62 813671
> 62. 34 935344
> 63. 146 1074072
>
> 64. 127 1232086
> 65. 84 1411912
> 66. 100 1616377
> ...
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