The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A340640 Perfect powers such that the two immediately adjacent perfect powers have at least one largest exponent A025479 greater than 2. 3
 4, 9, 25, 27, 32, 36, 49, 64, 81, 100, 121, 125, 128, 144, 196, 225, 243, 256, 289, 324, 361, 484, 529, 576, 676, 784, 961, 1000, 1024, 1089, 1225, 1296, 1331, 1369, 1681, 1764, 2025, 2116, 2187, 2197, 2209, 2304, 2500, 2704, 2809, 3025, 3136, 3364, 3481, 3969 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..50. EXAMPLE a(1) = 4 because the next perfect power is 8 = 2^3, i.e., its exponent is > 2. a(2) = 9: the exponents of the neighbors 8 = 2^3 and 16 = 2^4 are both > 2. 16 is not in the sequence because both neighboring perfect powers 9 = 3^2 and 25 = 5^2 have exponents 2. Neighbors with exponents > 2 of the next terms: a(3) = 25 (16 = 2^3), a(4) = 27 (32 = 2^5), a(5) = 32 (27 = 3^3), a(6) = 36 (32 = 2^5), a(7) = 49 (64 = 2^6), a(8) = 64 (81 = 3^4). PROG (PARI) a340640(limit)={my(p2=999, p1=2, n2=1, n1=4); for(n=5, limit, my(p0=ispower(n)); if(p0>1, if(p2+p0>4, print1(n1, ", ")); n2=n1; n1=n; p2=p1; p1=p0))}; a340640(5000) CROSSREFS Cf. A000290, A001597, A025479, A111245, A153158, A340586, A340641. Sequence in context: A175119 A093867 A126638 * A073045 A045967 A336445 Adjacent sequences: A340637 A340638 A340639 * A340641 A340642 A340643 KEYWORD nonn AUTHOR Hugo Pfoertner, Jan 14 2021 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 19 18:05 EDT 2024. Contains 371798 sequences. (Running on oeis4.)