A379828 Ulam numbers that are oblong (or promic) numbers.

2, 6, 72, 182, 1406, 2550, 5550, 6806, 9120, 9702, 13572, 14520, 14762, 32580, 43890, 50400, 51756, 56882, 65280, 74802, 78680, 80940, 86142, 92112, 96410, 99540, 107256, 115940, 120062, 120756, 129240, 134322, 138012, 139502, 154842, 179352, 193160, 199362, 224202, 251502, 259590, 278256

Offset

1,1

Links

Matthew L. LaSelle, Table of n, a(n) for n = 1..61 (first 42 terms from Massimo Kofler)

Example

2 is a term because 2 = 1*2 and 2 is an Ulam number.
6 is a term because 6 = 2*3 and 6 is an Ulam number.
72 is a term because 72 = 8*9 and 72 is an Ulam number.

Mathematica

seq[numUlams_] := Module[{ulams = {1, 2}}, Do[AppendTo[ulams, n = Last[ulams]; While[n++; Length[DeleteCases[Intersection[ulams, n - ulams], n/2, 1, 1]] != 2]; n], {numUlams}]; Select[ulams, IntegerQ[Sqrt[4*# + 1]] &]]; seq[10000] (* Amiram Eldar, Jan 03 2025, after Jean-François Alcover at A002858 *)

Crossrefs

Intersection of A002378 and A002858.

Sequence in context: A239543 A180982 A195690 * A359365 A329965 A171582

Adjacent sequences: A379825 A379826 A379827 * A379829 A379830 A379831

Keyword

nonn

Author

Massimo Kofler, Jan 03 2025

Status

approved