A377949 Numbers k such that k | A377484(k) and (k+1) | A377484(k+1).

156519, 245024, 310155, 524799, 638000, 893024, 1079000, 2055780, 2095975, 2203200, 2566025, 2592512, 2853135, 2934063, 3213375, 3294719, 4056975, 4322240, 4471935, 5746455, 6515145, 7289919, 7316000, 7329608, 7866495, 8459360, 8555624, 8934464, 9035415, 11291091

Offset: 1

Author

Amiram Eldar, Nov 12 2024

Keywords

• nonn

Comments

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

Examples

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

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A377484.

Subsequence of A056954.

Similar sequences: A355332, A377951, A377953.

Programs

Mathematica

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

PARI

is1(k) = if(k == 1, 1, my(d = divisors(k)); !(prod(i = 2, #d, d[i]-1) % k));
lista(kmax) = {my(q1 = is1(1), q2); for(k = 2, kmax, q2 = is1(k); if(q1 && q2, print1(k-1, ", ")); q1 = q2);}