A112392 -id:A112392 - cp's OEIS frontend

A112393 Semiprimes n such that 3*n - 2 is a square.

6, 9, 22, 34, 57, 86, 121, 134, 177, 209, 226, 262, 321, 386, 482, 706, 737, 1046, 1241, 1282, 1366, 1497, 1681, 1977, 2582, 2641, 2761, 3202, 3334, 3401, 3746, 3817, 3961, 4034, 4486, 4881, 5377, 5462, 5721, 6166, 6722, 6817, 7009, 7401, 7601, 7702, 8857

Offset: 1

Giovanni Teofilatto, Dec 05 2005

nonn

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A112392.

Select[Range[10000],PrimeOmega[#]==2&&IntegerQ[Sqrt[3#-2]]&] (* Harvey P. Dale, Mar 28 2018 *)

for(i=1,15000,if(bigomega(i)==2&&issquare(3*i-2),print1(i,","))) (Herrgesell)

More terms from Lambert Herrgesell (zero815(AT)googlemail.com), Dec 12 2005

A124106 Octagonal numbers equal to S*(3S - 2) with 3S - 2 = k^2 and S semiprime.

Original entry on oeis.org

96, 225, 1408, 3400, 9633, 22016, 43681, 53600, 93633, 130625, 152776, 205408, 308481, 446216, 696008, 1493896, 1628033, 3280256, 4617761, 4928008, 5595136, 6720033, 8473921, 11721633, 19995008, 20919361, 22863841, 30752008, 33340000

Offset: 1

Giovanni Teofilatto, Dec 13 2006, Dec 14 2006

Eric Weisstein's World of Mathematics, Octagonal Number.
Eric Weisstein's World of Mathematics, Semiprime.
Eric Weisstein's World of Mathematics, 16-Cell

Cf. A112392, A112393.

a(n) = A112392(n)*A112393(n).

cp's OEIS Frontend

A112393 Semiprimes n such that 3*n - 2 is a square.

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