

A208247


Numbers having exactly one partition into two prime powers.


2



2, 3, 119, 127, 163, 179, 191, 193, 217, 219, 221, 223, 239, 251, 269, 311, 337, 343, 389, 403, 415, 419, 427, 431, 457, 491, 505, 547, 557, 569, 575, 581, 583, 597, 599, 613, 653, 659, 667, 671, 673, 683, 697, 719, 739, 749, 767, 779, 787, 799, 807, 817
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OFFSET

1,1


COMMENTS

A071330(a(n)) = 1.


LINKS

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


PROG

(Haskell)
a095841 n = a095841_list !! (n1)
a095841_list = filter ((== 1) . a071330) a000961_list
(PARI) is(n)=sum(i=2, n\2, isprimepower(i)&&isprimepower(ni))+isprimepower(n1)==1  n==2 \\ naive; Charles R Greathouse IV, Nov 21 2014
(PARI) is(n)=my(s); forprime(p=2, n\2, if(isprimepower(np) && s++>1, return(0))); for(e=2, log(n)\log(2), forprime(p=2, sqrtnint(n\2, e), if(isprimepower(np^e) && s++>1, return(0)))); s+(!!isprimepower(n1))==1  n==2 \\ faster; Charles R Greathouse IV, Nov 21 2014


CROSSREFS

A095841 = Intersection of A208247 and A000961.
Sequence in context: A215238 A127819 A152838 * A102697 A041813 A065842
Adjacent sequences: A208244 A208245 A208246 * A208248 A208249 A208250


KEYWORD

nonn


AUTHOR

Reinhard Zumkeller, Jan 11 2013


STATUS

approved



