A208247 Numbers having exactly one partition into two prime powers.

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

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: A371146 A127819 A152838 * A102697 A041813 A065842

Adjacent sequences: A208244 A208245 A208246 * A208248 A208249 A208250

Keyword

nonn

Author

Reinhard Zumkeller, Jan 11 2013

Status

approved