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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 (list; graph; refs; listen; history; text; internal format)
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 !! (n-1)

a095841_list = filter ((== 1) . a071330) a000961_list

(PARI) is(n)=sum(i=2, n\2, isprimepower(i)&&isprimepower(n-i))+isprimepower(n-1)==1 || n==2 \\ naive; Charles R Greathouse IV, Nov 21 2014

(PARI) is(n)=my(s); forprime(p=2, n\2, if(isprimepower(n-p) && s++>1, return(0))); for(e=2, log(n)\log(2), forprime(p=2, sqrtnint(n\2, e), if(isprimepower(n-p^e) && s++>1, return(0)))); s+(!!isprimepower(n-1))==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

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Last modified December 15 00:30 EST 2019. Contains 329988 sequences. (Running on oeis4.)