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Search: id:A131787
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| A131787 |
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a(n) = a(n-1) + (number of terms, from among the first (n-1) terms of the sequence, which are coprime to the n-th Fibonacci number). |
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+0
2
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| 1, 2, 3, 5, 8, 11, 17, 23, 28, 35, 45, 51, 63, 76, 83, 92, 108, 117, 135, 144, 156, 177, 199, 205, 224, 249, 264, 279, 307, 319, 349, 364, 385, 418, 443, 456, 492, 529, 553, 566, 606, 629, 671, 696, 713, 758, 804, 817, 862, 899, 929, 962, 1014, 1041, 1089, 1114
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OFFSET
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1,2
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EXAMPLE
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The 6th Fibonacci number is 8. Of the first 5 terms, only terms a(1)=1, a(3)=3, and a(4) = 5 are coprime to 8. Since there are 3 such terms, a(6) = a(5) + 3 = 11.
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MAPLE
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with(combinat): a[1]:= 1: for n from 2 to 55 do ct := 0: for j to n-1 do if gcd(a[j], fibonacci(n)) = 1 then ct := ct+1 else ct := ct end if end do: a[n]:= a[n-1]+ct end do: seq(a[n], n = 1 .. 55); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 24 2007
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CROSSREFS
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Cf. A131788.
Sequence in context: A039847 A046938 A060677 this_sequence A091498 A000511 A135908
Adjacent sequences: A131784 A131785 A131786 this_sequence A131788 A131789 A131790
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Jul 15 2007
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EXTENSIONS
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More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org) and Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 18 2007
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