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%I #33 Oct 04 2022 12:36:08
%S 1,3,4,7,6,12,8,15,13,18,12,28,14,24,24,31,18,39,20,42,32,36,24,60,31,
%T 42,40,56,30,72,32,63,48,54,48,91,38,60,56,90,42,96,44,84,78,72,48,
%U 124,8,93,72,98,54,120,72,120,80,90,60,168,62,96,104,127,84,144
%N Sum of the divisors of n that are not divisible by 49.
%H Seiichi Manyama, <a href="/A287926/b287926.txt">Table of n, a(n) for n = 1..10000</a>
%F Multiplicative with a(7^e) = 8 and a(p^e) = (p^(e+1)-1)/(p-1) otherwise. - _Amiram Eldar_, Sep 17 2020
%F Sum_{k=1..n} a(k) ~ (4*Pi^2/49) * n^2. - _Amiram Eldar_, Oct 04 2022
%t f[p_, e_] := If[p == 7, 8, (p^(e+1)-1)/(p-1)]; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Sep 17 2020 *)
%o (PARI) a(n)=sumdiv(n, d, ((d%49)>0)*d); \\ _Andrew Howroyd_, Jul 20 2018
%Y Cf. A000203, A213598.
%Y Sum of the divisors of n that are not divisible by k: A046913 (k=3), A046897 (k=4), A116073 (k=5), A284326 (k=6), A113957 (k=7), A284341 (k=8), A116607 (k=9), A284344 (k=10), A227131 (k=25), this sequence (k=49).
%K nonn,mult
%O 1,2
%A _Seiichi Manyama_, Jun 15 2017
%E Keyword:mult added by _Andrew Howroyd_, Jul 20 2018
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