A193164 - OEIS

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

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A193164

a(1) = 1 ; for n > 1, a(n) is the smallest number such that a(n)^2 + 1 contains n distinct prime divisors dividing a(n+1)^2 + 1.

1, 3, 13, 47, 463, 25683, 4187997

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

This sequence is not the same as A180278.

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

a(1) = 1^1 + 1 = 2 ;

a(2) = 3^2 + 1 = 2*5 ;

a(3) = 13^2 + 1 = 2*5*17 ;

a(4) = 47^2 + 1 = 2*5*13*17 ;

a(5) = 463^2 + 1 = 2*5*13*17*97 ;

a(6) = 25683^2 + 1 = 2 * 5 * 13 * 17 ^ 2 * 97 * 181 ;

a(7) = 4187997^2 + 1 = 2 * 5 * 13 * 17 * 97 * 181 * 452033.

MAPLE

with(numtheory):A:={2}:for n from 1 to 7 do:id:=0:for k from 1 to 4200000 (id=0) do:x:=k^2+1:y:=factorset(x):n1:=nops(y):if n1=n and A intersect y = A then A:=y:id:=1:printf ( "%d %d \n", n, k):else fi:od:od:

CROSSREFS

Cf. A180278.

Sequence in context: A265920 A262322 A180278 * A122424 A027326 A108946

Adjacent sequences: A193161 A193162 A193163 * A193165 A193166 A193167

KEYWORD

nonn

AUTHOR

Michel Lagneau, Jul 17 2011

STATUS

approved