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A121940 Product of the first n primes of the form 6k+1. 9
7, 91, 1729, 53599, 1983163, 85276009, 5201836549, 348523048783, 25442182561159, 2009932422331561, 194963444966161417, 20081234831514625951, 2188854596635094228659, 277984533772656967039693, 38639850194399318418517327, 5834617379354297081196116377 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n>1, a(n) is the least positive integer that can be primitively represented as m^2+mn+n^2 with 0<=m<=n and gcd(m,n)=1 in exactly 2^(n-1) ways. - Ray Chandler, Oct 01 2007

LINKS

Ray Chandler, Table of n, a(n) for n=1..100

FORMULA

a(n) = Product_{i=1..n} A002476(i).

EXAMPLE

a(4) = 53599 = 7 * 13 * 19 * 31.

MATHEMATICA

Rest@FoldList[Times, 1, Select[6 Range[100] + 1, PrimeQ]] (* Ray Chandler, Oct 01 2007 *)

PROG

(PARI) lista(nn) = {my(pr=1, list=List()); forprime(p=1, nn, if ((p%3) == 1, listput(list, pr *= p)); ); Vec(list); } \\ Michel Marcus, Jul 17 2020

CROSSREFS

Cf. A002476, A002110, A006278, A078586.

Greedy inverse of A005088.

Sequence in context: A113372 A131940 A008542 * A177784 A326266 A124557

Adjacent sequences:  A121937 A121938 A121939 * A121941 A121942 A121943

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Sep 03 2006

EXTENSIONS

Extended by Ray Chandler, Oct 01 2007

STATUS

approved

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Last modified August 12 03:34 EDT 2020. Contains 336436 sequences. (Running on oeis4.)