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A173083 Semiprimes q such that q^2+3 and q^2-3 are also semiprimes. 4
6, 226, 262, 302, 314, 334, 346, 382, 466, 482, 514, 538, 562, 734, 778, 842, 866, 886, 898, 926, 974, 1006, 1046, 1282, 1306, 1318, 1322, 1438, 1466, 1478, 1574, 1622, 1774, 1822, 1838, 1858, 1894, 1994, 2302, 2342, 2446, 2518, 2578, 2582, 2602, 2638 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..46.

FORMULA

{A001358(j): A074985(j)-3 in A001358 and A074985(j)+3 in A001358}. [R. J. Mathar, Mar 11 2010]

EXAMPLE

6^2-3=33 = 3*11 and 6^2+3=39 = 3*13 are semiprimes derived from q=6, so q=6 is in the sequence.

MATHEMATICA

f[n_]:=Last/@FactorInteger[n]=={1, 1}||Last/@FactorInteger[n]=={2}; lst={}; Do[If[f[n], a=n^2-3; b=n^2+3; If[f[a]&&f[b], AppendTo[lst, n]]], {n, 8!}]; lst

CROSSREFS

Cf. A001358, A173082

Sequence in context: A223100 A233142 A166502 * A084070 A282736 A277293

Adjacent sequences:  A173080 A173081 A173082 * A173084 A173085 A173086

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Feb 09 2010

EXTENSIONS

Definition rephrased - R. J. Mathar, Mar 11 2010

STATUS

approved

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Last modified September 21 12:35 EDT 2019. Contains 327253 sequences. (Running on oeis4.)