

A073630


Numbers k such that k*(prime(k)  1) is a square.


0



1, 2, 8, 1849, 22912, 40328, 646912, 3607298, 6323422, 7520900, 8962893, 23879700, 38043325, 157944268, 1105942626, 3604734726, 5239828426, 8179002096, 8179002106, 37234260225
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OFFSET

1,2


COMMENTS



LINKS



EXAMPLE

7520900*(prime(7520900)  1) = 997787845328400 = 31587780^2 is a perfect square, so 7520900 is in the sequence.


MATHEMATICA

Do[k = n*Prime[n]  n; If[IntegerQ[Sqrt[k]], Print[n]], {n, 1, 670000000}] (* Ryan Propper, Aug 24 2005 *)


PROG

(PARI) isok(k) = issquare(k*(prime(k)1)); \\ Michel Marcus, Feb 15 2021


CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR



EXTENSIONS



STATUS

approved



