Revision History for A083917
(Underlined text is an addition;
strikethrough text is a deletion.)
Showing entries 1-10
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#14 by OEIS Server at Sat Dec 30 09:33:54 EST 2023
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Amiram Eldar, <a href="/A083917/b083917_1.txt">Table of n, a(n) for n = 1..10000</a>
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#13 by Michael De Vlieger at Sat Dec 30 09:33:54 EST 2023
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Discussion
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| OEIS Server: Installed first b-file as b083917.txt.
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#12 by Joerg Arndt at Sat Dec 30 03:27:39 EST 2023
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#11 by Amiram Eldar at Sat Dec 30 03:05:32 EST 2023
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#10 by Amiram Eldar at Sat Dec 30 02:47:41 EST 2023
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Amiram Eldar, <a href="/A083917/b083917_1.txt">Table of n, a(n) for n = 1..10000</a>
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#9 by Amiram Eldar at Sat Dec 30 02:47:07 EST 2023
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R. A. Smith and M. V. Subbarao, <a href="https://doi.org/10.4153/CMB-1981-005-3">The average number of divisors in an arithmetic progression</a>, Canadian Mathematical Bulletin, Vol. 24, No. 1 (1981), pp. 37-41.
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| FORMULA
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Sum_{k=1..n} a(k) = n*log(n)/10 + c*n + O(n^(1/3)*log(n)), where c = gamma(7,10) - (1 - gamma)/10 = -0.150534..., gamma(7,10) = -(psi(7/10) + log(10))/10 is a generalized Euler constant, and gamma is Euler's constant (A001620) (Smith and Subbarao, 1981). - Amiram Eldar, Dec 30 2023
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| MATHEMATICA
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a[n_] := DivisorSum[n, 1 &, Mod[#, 10] == 7 &]; Array[a, 100] (* Amiram Eldar, Dec 30 2023 *)
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| PROG
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(PARI) a(n) = sumdiv(n, d, d % 10 == 7); \\ Amiram Eldar, Dec 30 2023
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| CROSSREFS
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Cf. A010879, A000005, A001227, A010879.
Cf. A001620, A002392, A354643 (psi(7/10)).
Cf. A083910, A083911, A083912, A083913, A083914, A083915, A083916, A083918, A083919.
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| KEYWORD
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nonn,easy
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| STATUS
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approved
editing
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#8 by Harvey P. Dale at Fri Sep 15 15:21:04 EDT 2023
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#7 by Harvey P. Dale at Fri Sep 15 15:21:00 EDT 2023
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Table[Count[Divisors[n], _?(Mod[#, 10]==7&)], {n, 110}] (* Harvey P. Dale, Sep 15 2023 *)
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approved
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#6 by Alois P. Heinz at Wed Sep 11 12:09:43 EDT 2019
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#5 by Ilya Gutkovskiy at Wed Sep 11 12:09:00 EDT 2019
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