A082949 - OEIS

A082949

Numbers of the form p^q * q^p, with distinct primes p and q.

72, 800, 6272, 30375, 247808, 750141, 1384448, 37879808, 189267968, 235782657, 1313046875, 3502727631, 4437573632, 451508436992, 634465620819, 2063731785728, 7863818359375, 7971951402153, 188153927303168, 453238525390625, 1145440056788109

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OFFSET

1,1

COMMENTS

A001221(a(n)) = 2;

A001222(a(n)) = A001414(a(n)) = A020639(a(n)) + A006530(a(n)) = A051904(a(n)) + A051903(a(n));

A020639(a(n)) = A051904(a(n));

A006530(a(n)) = A051903(a(n)).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

EXAMPLE

2^7 * 7^2 = 128*49 = 6272, therefore 6272 is in the sequence.

MATHEMATICA

Take[Union[Select[Flatten[Table[If[p != q, Prime[p]^Prime[q]*Prime[q]^Prime[p]], {p, 100}, {q, 100}]], IntegerQ]], 30] (* Alonso del Arte, Oct 28 2005 *)

Select[Range[10! ], Length[FactorInteger[ # ]]==2&&FactorInteger[ # ][[1, 1]]==FactorInteger[ # ][[2, 2]]&&FactorInteger[ # ][[1, 2]]==FactorInteger[ # ][[2, 1]]&] (* Vladimir Joseph Stephan Orlovsky, Apr 23 2010 *)

With[{nn=30}, Take[Union[First[#]^Last[#] Last[#]^First[#]&/@ Subsets[ Prime[Range[nn]], {2}]], nn]] (* Harvey P. Dale, Aug 19 2012 *)

PROG

(PARI) term(p, q)=p^q*q^p;

l=listcreate(465); for(m=1, 30, for(n=m+1, 31, listput(l, term(prime(m), prime(n))))); listsort(l) \\ Rick L. Shepherd, Sep 07 2003

(Haskell)

import Data.Set (singleton, deleteFindMin, insert)

a082949 n = a082949_list !! (n-1)

a082949_list = f $ singleton (2 ^ 3 * 3 ^ 2, 2, 3) where

f s = y : f (if p' < q then insert (p' ^ q * q ^ p', p', q) s'' else s'')

where s'' = insert (p ^ q' * q' ^ p, p, q') s'

p' = a151800 p; q' = a151800 q

((y, p, q), s') = deleteFindMin s