

A216303


Numbers k such that 10k+1 and 10k+3 are prime but 10k+7 and 10k+9 are composite.


1



28, 52, 115, 172, 193, 211, 214, 259, 280, 337, 358, 382, 385, 424, 427, 442, 448, 502, 613, 655, 676, 679, 733, 901, 928, 1027, 1030, 1135, 1207, 1216, 1225, 1393, 1456, 1459, 1558, 1597, 1645, 1663, 1690, 1768, 1813, 1831, 1852, 1918, 1954, 1984, 1996, 2023
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OFFSET

1,1


LINKS

V. Raman, Table of n, a(n) for n = 1..10000


FORMULA

a(n) >> n log^2 n.  Charles R Greathouse IV, Sep 07 2012


EXAMPLE

28 is a member since 281 & 283 are prime while 287 & 289 are composite.


MATHEMATICA

t = {}; Do[ps = Select[Range[10*n, 10*n + 9], PrimeQ]; If[ps == {10*n + 1, 10*n + 3}, AppendTo[t, n]], {n, 0, 2689}]; t (* T. D. Noe, Sep 04 2012 *)
Select[Range[2100], PrimeQ[10#+{1, 3, 7, 9}]=={True, True, False, False}&] (* Harvey P. Dale, Dec 17 2014 *)


CROSSREFS

Cf. A032352, A007811, A078494.
Sequence in context: A181792 A181793 A224545 * A261105 A043134 A039311
Adjacent sequences: A216300 A216301 A216302 * A216304 A216305 A216306


KEYWORD

nonn


AUTHOR

V. Raman, Sep 03 2012


EXTENSIONS

Definition corrected by Harvey P. Dale, Dec 17 2014


STATUS

approved



