The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A309263 Terms of A140110 that are not divisible by 6. 0
 1, 2, 4, 8, 16, 20, 32, 64, 100, 128, 256, 272, 500, 512, 1024, 2048, 2500, 4096, 4624, 8192, 10100, 12500, 16384, 32768, 62500, 65536, 65792, 78608, 131072, 262144, 312500, 524288, 1020100, 1048576, 1336336, 1562500, 2097152, 4194304, 7812500, 8388608 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Includes all powers of 2. Conjecture: The sequence includes all numbers of the form 4*5^n. The number 10100 is a counterexample for: (a) Prime factorizations of numbers of this sequence will always have only 2's and Fermat primes. (b) No number in this sequence is divisible by more than one distinct odd prime. LINKS EXAMPLE 20 is in this sequence because it is in A140110 and is not divisible by 6. 24, which is in A140110, is not in this sequence because it is divisible by 6. PROG (PARI) isok(n) = {if(n%6 == 0, return(0)); my(d = divisors(n)); for (k=1, #d - 1, r = d[k+1]/d[k]; if(numerator(r) != denominator(r) + 1, return(0)); ); return(1); } \\ Jinyuan Wang, Aug 03 2019 CROSSREFS Cf. A140110, A000079, A005054. Sequence in context: A093107 A125508 A067945 * A166156 A089473 A118021 Adjacent sequences:  A309260 A309261 A309262 * A309264 A309265 A309266 KEYWORD nonn AUTHOR J. Lowell, Jul 19 2019 STATUS approved

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

Last modified May 8 19:52 EDT 2021. Contains 343668 sequences. (Running on oeis4.)