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Cf. . A221918, A000027 (m=1), A145979(m=2), A221920 (m=3), A221921 (m=4).

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Michel Marcus: just removed a blank

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<a href="/index/Rec#order_50">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,-1).

Sum_{k=5..n} a(k) ~ (521/250) * n^2. - Amiram Eldar, Oct 09 2023

a(n) = n*5/gcd(n*5,n+5), n >= 5.

a(n) = 2*a(n-25)-a(n-50). [_). - _Colin Barker_, Feb 25 2013]

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Table[(5n)/GCD[5n, n +5], {n, 5, 60}] (* Harvey P. Dale, Nov 06 2020 *)

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