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Number of divisors d of n such that (d+1) is a divisor of (n+1) and (d+2) a divisor of (n+2).
2

%I #13 Jun 03 2022 03:21:55

%S 1,1,1,1,1,1,2,1,1,1,1,1,2,2,1,1,1,1,2,1,1,1,1,1,2,2,1,1,1,1,2,1,1,1,

%T 1,1,2,2,1,1,1,1,2,1,1,1,1,1,2,2,1,1,1,1,2,1,1,1,1,1,2,2,2,2,1,1,2,1,

%U 1,1,1,1,2,2,1,1,1,1,2,1,1,1,1,1,2,2,1,1,1,1,2,1,1,1,1,1,2,2,1,1,1,1,2,1,1

%N Number of divisors d of n such that (d+1) is a divisor of (n+1) and (d+2) a divisor of (n+2).

%H Antti Karttunen, <a href="/A082478/b082478.txt">Table of n, a(n) for n = 1..65537</a>

%F a(2^n-1) = A001227(n).

%t a[n_] := DivisorSum[n, 1 &, Divisible[n+1, #+1] && Divisible[n+2, #+2] &]; Array[a, 100] (* _Amiram Eldar_, Jun 03 2022 *)

%o (PARI) a(n)=sumdiv(n,d,if((n+1)%(d+1)+(n+2)%(d+2),0,1))

%Y Cf. A001227, A082477.

%K nonn

%O 1,7

%A _Benoit Cloitre_, Apr 27 2003