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%I #23 Jul 28 2024 10:07:54
%S 1,2,4,6,8,12,16,24,30,32,36,48,60,72,96,128,180,192,210,240,256,360,
%T 384,420,432,480,576,720,768,840,864,1152,1260,1296,1440,1800,2160,
%U 2310,2520,2592,2880,3360,3456,4620,5040,5400,6144,6300,6480,6720,6912,7560
%N Numbers k of least prime signature (A025487) such that k-1 or k+1 is prime.
%C The corresponding prime numbers are A344384.
%C 64 is the first number of least prime signature not in this sequence.
%C Questions: 1) Is this sequence infinite? 2) Is log(a(n)) = O(log(n)^2)? For the first 132 terms, log(a(n)) is fit unusually well by a quadratic polynomial in log(n).
%H Amiram Eldar, <a href="/A344385/b344385.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..132 from Hal M. Switkay)
%e 16 is a term because 16 is in A025487 and 16 + 1 is prime.
%t (* Load the function f[n] at A025487, then: *)
%t Select[Union@ Flatten@ f[6], AnyTrue[# + {-1, 1}, PrimeQ] &]
%t (* or use the b-file at A025487: *)
%t Select[TakeWhile[Import["https://oeis.org/A025487/b025487.txt", "Data"], Length@ # == 2 &][[All, -1]], AnyTrue[# + {-1, 1}, PrimeQ] &] (* _Michael De Vlieger_, May 16 2021 *)
%Y Cf. A000040, A025487, A344384.
%K nonn
%O 1,2
%A _Hal M. Switkay_, May 16 2021