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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A253204 a(1) = 1; for n>1, a(n) is a prime power p^h (h>=1) with the property that its k-th smallest divisor, for all 1 <= k <= tau(p^h), contains exactly k "1" digits in its binary representation. 1
 1, 3, 5, 17, 25, 257, 289, 65537, 66049, 4295098369 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Supersequence of A019434 (Fermat primes). Subsequence of A071593 and A255401. Sequence is finite if there is only 5 Fermat primes (A019434). LINKS Table of n, a(n) for n=1..10. EXAMPLE The divisors of 4295098369, expressed in base 2 and listed in ascending order as 1, 10000000000000001, 100000000000000100000000000000001, contain 1, 2 and 3, "1" digits, respectively. PROG (Magma) Set(Sort([1] cat [n: n in [2..1000000] | [&+Intseq(d, 2): d in Divisors(n)] eq [1..NumberOfDivisors(n)] and #(PrimeDivisors(n)) eq 1])) CROSSREFS Cf. A019434, A071593, A255401. Sequence in context: A323194 A024867 A025111 * A266165 A281622 A256439 Adjacent sequences: A253201 A253202 A253203 * A253205 A253206 A253207 KEYWORD nonn,base AUTHOR Jaroslav Krizek, Mar 25 2015 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 June 1 15:36 EDT 2023. Contains 363074 sequences. (Running on oeis4.)