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A362404
Numbers k such that k and k+1 are both in A362401.
2
24, 27, 48, 79, 120, 168, 199, 288, 350, 360, 378, 391, 447, 507, 528, 775, 840, 895, 960, 1088, 1136, 1368, 1638, 1639, 1680, 1848, 1849, 2095, 2127, 2208, 2322, 2749, 2808, 3720, 3726, 3798, 3799, 3919, 4050, 4087, 4488, 4550, 4872, 5040, 5328, 5448, 5631, 6240
OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..3557 (terms below 10^8)
EXAMPLE
24 is a term since 24 and 25 are both in the range of A162296: A162296(20) = 24 and A162296(25) = 25.
MATHEMATICA
s[n_] := Module[{f = FactorInteger[n], p, e}, p = f[[;; , 1]]; e = f[[;; , 2]]; Times @@ ((p^(e + 1) - 1)/(p - 1)) - Times @@ (p + 1)]; s[1] = 0; seq[max_] := Module[{v = Select[Union[Array[s, max]], 0 < # <= max &], i}, i = Position[Differences[v], 1] // Flatten; v[[i]]]; seq[10^4]
PROG
(PARI) s(n) = {my(f = factor(n), p, e); prod(i = 1, #f~, p = f[i, 1]; e = f[i, 2]; ((p^(e + 1) - 1)/(p - 1))) - prod(i = 1, #f~, f[i, 1] + 1); }
lista(kmax) = {my(v = select(x -> (x < kmax), Set(vector(kmax, k, s(k))))); for(k=1, #v-1, if(v[k+1] - v[k] == 1, print1(v[k], ", "))); }
CROSSREFS
Subsequence of A362401.
A362405 is a subsequence.
Cf. A162296.
Sequence in context: A162465 A067193 A095235 * A316725 A164778 A268540
KEYWORD
nonn
AUTHOR
Amiram Eldar, Apr 18 2023
STATUS
approved