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A081312 Numbers having a unique representation as sum of a prime and an 3-smooth number. 4
3, 24, 28, 42, 48, 52, 54, 58, 60, 66, 72, 90, 102, 108, 114, 132, 138, 150, 168, 172, 174, 180, 192, 196, 198, 214, 228, 234, 240, 246, 252, 264, 268, 270, 282, 294, 298, 312, 318, 348, 354, 360, 384, 390, 402, 404, 420, 432, 444, 450, 462, 468, 478, 480, 492 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A081308(a(n))=1.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

MATHEMATICA

sp3sQ[n_]:=Length[Select[IntegerPartitions[n, {2}], (PrimeQ[#[[1]]]&&Max[ FactorInteger[#[[2]]][[All, 1]]]<4)||(PrimeQ[#[[2]]]&&Max[ FactorInteger[ #[[1]]][[All, 1]]]<4)&]]==1; Select[Range[500], sp3sQ]/.(5->Nothing) (* Harvey P. Dale, Feb 05 2019 *)

PROG

(Haskell)

a081312 n = a081312_list !! (n-1)

a081312_list = filter ((== 1) . a081308) [1..]

-- Reinhard Zumkeller, Jul 04 2012

CROSSREFS

Cf. A000040, A003586, A081313, subsequence of A081311.

Sequence in context: A065430 A175471 A035409 * A123598 A106217 A267274

Adjacent sequences:  A081309 A081310 A081311 * A081313 A081314 A081315

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 17 2003

STATUS

approved

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Last modified July 29 12:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)