A285885 -id:A285885 - cp's OEIS frontend

A287612 Ulam numbers k such that 4*k is also an Ulam number.

1, 2, 4, 18, 114, 131, 180, 258, 324, 412, 431, 605, 646, 864, 1037, 1081, 1101, 1167, 1296, 1313, 1404, 1470, 1765, 1856, 1858, 1900, 1944, 2032, 2117, 2327, 2572, 2630, 2635, 2674, 2787, 2809, 2814, 2897, 3068, 3214, 3219, 3261, 3393, 3451, 3591, 3622, 3630

Offset: 1

Enrique Navarrete, May 27 2017

nonn

Cf. A002858, A068791, A285885.

(* First run one of the programs for A002858 to populate the ulams list *) A287612 = ulams; curr = 1; While[curr < Length[ulams] + 1, A287612[[curr]] = ulams[[curr]] * Boole[MemberQ[ulams, 4ulams[[curr]]]]; curr++]; DeleteCases[A287612, 0] (* Alonso del Arte, May 28 2017 *)

A287613 Ulam numbers u such that 5*u is also an Ulam number.

Original entry on oeis.org

36, 97, 138, 206, 358, 402, 722, 2816, 3205, 3725, 3918, 3962, 5020, 5516, 7461, 8368, 8756, 9193, 9621, 10247, 11219, 11586, 11759, 12365, 12580, 12602, 13164, 13401, 14892, 15820, 17743, 18305, 19644, 20140, 22344, 24785, 29733, 32626, 33276, 34549, 34615, 35888

Offset: 1

Enrique Navarrete, May 27 2017

nonn

As in the case k=2, these are very scarce Ulam numbers u with the property that k*u is also an Ulam number (see link).

Enrique Navarrete, Relative Frequencies of Multiples of Ulam Numbers

Cf. A002858, A068791, A285885, A287612.

cp's OEIS Frontend

A287612 Ulam numbers k such that 4*k is also an Ulam number.

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A287613 Ulam numbers u such that 5*u is also an Ulam number.

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