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A231968 Squarefree numbers (A005117) of the form p*q*r*s with prime factors p, q, r, s with q = 2*p + 1, r = 2*q + 1 and s = 2*r + 1. 3
2530, 59455, 4112125651, 66487065301, 1069364586601, 4313828719351, 146264252084551, 252626415665851, 3398860950259501, 10045301361318901, 110736954977078251 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

4112125651 = 89*179*359*719; 179 = 2*89 + 1; 359 = 2*179 + 1, 719 = 2*359 + 1.

CROSSREFS

Cf. A005117, A000040, A231967, A231969, A231966.

Sequence in context: A252288 A268332 A203440 * A172142 A206596 A334932

Adjacent sequences:  A231965 A231966 A231967 * A231969 A231970 A231971

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Nov 18 2013

STATUS

approved

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Last modified December 5 17:28 EST 2021. Contains 349557 sequences. (Running on oeis4.)