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!)
 A261367 Number of nodes at level n in Euclid-Mullin graph starting with 1. 0
 1, 1, 1, 1, 1, 2, 4, 9, 24, 52, 165, 555, 2020 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS The Euclid-Mullin graph encodes all instances of Euclid's proof of the infinitude of primes. This sequences gives the number of nodes appearing at each level in the graph, when starting the graph from 1. a(13) is almost certainly 7950 but requires the factorization of a 253-digit number to confirm. LINKS Andrew R. Booker and Sean A. Irvine, The Euclid-Mullin Graph, to appear (2015). EXAMPLE Level 0 contains the single node 1, so a(0)=1. Level 1 contains the prime factors of 1+1, i.e., 2, so a(1)=2. The first interesting level is Level 5, which has the factors of 1*2*3*7*43+1 which are 13 and 139, hence a(5)=2. At higher levels there can be more than one path from a node back to the root. CROSSREFS Cf. A000945, A000946. Sequence in context: A080376 A005669 A038664 * A148077 A148078 A093156 Adjacent sequences:  A261364 A261365 A261366 * A261368 A261369 A261370 KEYWORD nonn,hard,more AUTHOR Sean A. Irvine, Aug 16 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 5 18:48 EDT 2020. Contains 334854 sequences. (Running on oeis4.)