

A344385


Numbers k of least prime signature (A025487) such that k1 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
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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 bfile 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



