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A287926 Sum of the divisors of n that are not divisible by 49. 3

%I

%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

%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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Last modified March 2 12:21 EST 2021. Contains 341750 sequences. (Running on oeis4.)