



30, 1309, 50209, 299423, 4329769, 4661471, 13968601, 19867823, 49402237, 90419171, 95575609, 230236057, 289003081, 4195692049, 7752275351, 8857002097, 9759031489, 10956612769, 12930672109, 12991059409, 13494943703, 13807499677, 15195694009, 18253659551, 20769940297
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OFFSET

1,1


COMMENTS

Golden 3almost primes.
Volumes of bricks (rectangular parallelopipeds) each of whose faces has golden semiprime area. How long a chain is possible of the form p(1) * p(2) * p(3) * ... * p(n) where each successive pair of values are factors of a golden semiprime? That is, if Zumkeller's golden semiprimes are the 2dimensional case and the present sequence is the 3dimensional case, is there a maximum n for an ndimensional case?


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


EXAMPLE

30 = 2 * 3 * 5, where both 2*3=6 and 3*5=15 are golden semiprimes.
1309 = 7 * 11 * 17.
50209 = 23 * 37 * 59.


MATHEMATICA

f[p_] := Module[{x = GoldenRatio * p}, p1 = NextPrime[x, 1]; p2 = NextPrime[p1]; q = If[x  p1 < p2  x, p1, p2]; If[Abs[q  x] < 1, q, 0]]; g[p_] := Module[{ p1 = f[p]}, If[p1 == 0, 0, p2 = f[p1]; If[p2 == 0, 0, p*p1*p2]]]; seq={}; p=1; Do[p = NextPrime[p]; gp = g[p]; If[gp > 0, AppendTo[seq, gp]], {300}]; seq (* Amiram Eldar, Nov 29 2019 *)


CROSSREFS

Cf. A014612, A108540, A108541, A108542.
Sequence in context: A163521 A273416 A002456 * A048536 A318496 A000173
Adjacent sequences: A107765 A107766 A107767 * A107769 A107770 A107771


KEYWORD

easy,nonn


AUTHOR

Jonathan Vos Post, Jun 11 2005


EXTENSIONS

More terms from Amiram Eldar, Nov 29 2019


STATUS

approved



