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 A344385 Numbers k of least prime signature (A025487) such that k-1 or k+1 is prime. 2
 1, 2, 4, 6, 8, 12, 16, 24, 30, 32, 36, 48, 60, 72, 96, 128, 180, 192, 210, 240, 256, 360, 384, 420, 432, 480, 576, 720, 768, 840, 864, 1152, 1260, 1296, 1440, 1800, 2160, 2310, 2520, 2592, 2880, 3360, 3456, 4620, 5040, 5400, 6144, 6300, 6480, 6720, 6912, 7560 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The corresponding prime numbers are A344384. 64 is the first number of least prime signature not in this sequence. 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). LINKS Hal M. Switkay, Table of n, a(n) for n = 1..132 EXAMPLE 16 is a term because 16 is in A025487 and 16 + 1 is prime. MATHEMATICA (* Load the function f[n] at A025487, then: *) Select[Union@ Flatten@ f[6], AnyTrue[# + {-1, 1}, PrimeQ] &] (* or use the b-file at A025487: *) Select[TakeWhile[Import["https://oeis.org/A025487/b025487.txt", "Data"], Length@ # == 2 &][[All, -1]], AnyTrue[# + {-1, 1}, PrimeQ] &] (* Michael De Vlieger, May 16 2021 *) CROSSREFS Cf. A000040, A025487, A344384. Sequence in context: A333964 A279537 A325238 * A070175 A096850 A250270 Adjacent sequences:  A344382 A344383 A344384 * A344386 A344387 A344389 KEYWORD nonn AUTHOR Hal M. Switkay, May 16 2021 STATUS approved

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Last modified August 5 20:01 EDT 2021. Contains 346488 sequences. (Running on oeis4.)