OFFSET
1,1
COMMENTS
Empirically, there seem to be no intervals between consecutive squares containing more than two nonsquare perfect powers.
It is easy to see that two distinct powers between n^2 and (n+1)^2 are necessarily of the form x^p and y^q where p, q are distinct odd primes. Among the first 180 terms, only 4 are of type (p,q) = (3,7) and all others are of type (3,5). The first term with q = 11, if it exists, is > (1e6)^(11/2) = 1e33. - M. F. Hasler, Jan 18 2021
LINKS
T. D. Noe, Table of n, a(n) for n = 1..180 (using the b-file from A117934)
EXAMPLE
a(1) = 5: 5^2 < 3^3 < 2^5 < 6^2,
a(2) = 11: 11^2 < 5^3 < 2^7 < 12^2,
a(3) = 46: 46^2 = 2116 < 3^7 = 2187 < 13^3 = 2197 < 47^2 = 2209.
a(4) = 2536: 2536^2 = 6431296 < 186^3 = 6434856 < 23^5 = 6436343 < 2537^2 = 6436369.
22 is not in the sequence because 2^9 and 8^3 (22^2 < 512 < 23^2) are not distinct.
Also, 181 is not listed since between 181^2 and 182^2 there is only 32^3 = 8^5.
PROG
(PARI) is(n)=my(s, t); forprime(p=3, 2*log(n+1.5)\log(2), t=floor((n+1)^(2/p)); if(t^p>n^2 && !ispower(t) && s++ > 1, return(1))); 0 \\ Charles R Greathouse IV, Dec 11 2012
(PARI) haspow(lower, upper, eMin, eMax)=if(sqrtnint(upper, 3)^3>lower, return(1)); forprime(e=eMin, eMax, if(sqrtnint(upper, e)^e>lower, return(1))); 0
list(lim)=lim\=1; my(v=List(), M=(lim+1)^2, L=logint(M, 2), s); forprime(e=5, L, forprime(p=2, sqrtnint(M, e), s=sqrtint(p^e); if(haspow(s^2, (s+1)^2-1, e+1, L) && s<=lim, listput(v, s)))); Set(v) \\ Charles R Greathouse IV, Nov 05 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Jul 21 2004
EXTENSIONS
a(5)-a(20) from Don Reble
a(21)-a(26) from David Wasserman, Dec 17 2007
STATUS
approved