A377949 - OEIS

%I #10 Nov 13 2024 17:22:30

%S 156519,245024,310155,524799,638000,893024,1079000,2055780,2095975,

%T 2203200,2566025,2592512,2853135,2934063,3213375,3294719,4056975,

%U 4322240,4471935,5746455,6515145,7289919,7316000,7329608,7866495,8459360,8555624,8934464,9035415,11291091

%N Numbers k such that k | A377484(k) and (k+1) | A377484(k+1).

%C Numbers k such that k and k+1 are both terms in A056954.

%H Amiram Eldar, <a href="/A377949/b377949.txt">Table of n, a(n) for n = 1..1000</a>

%e 156519 is a term since A377484(156519) is divisible by 156519 and A377484(156520) is divisible by 156520.

%t q[n_] := q[n] = Divisible[Times @@ (Rest@ Divisors[n] - 1), n]; Select[Range[10^6], q[#] && q[#+1] &]

%o (PARI) is1(k) = if(k == 1, 1, my(d = divisors(k)); !(prod(i = 2, #d, d[i]-1) % k));

%o lista(kmax) = {my(q1 = is1(1), q2); for(k = 2, kmax, q2 = is1(k); if(q1 && q2, print1(k-1, ", ")); q1 = q2);}

%Y Cf. A377484.

%Y Subsequence of A056954.

%Y Similar sequences: A355332, A377951, A377953.

%K nonn

%O 1,1

%A _Amiram Eldar_, Nov 12 2024