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 A193869 Smallest product of n distinct primes of the form n*k + 1. 5
 2, 15, 1729, 32045, 60551711, 85276009, 52814801041129, 1312422595226609, 1130308388231798179, 4182230628909121261, 100166053986652515419641469, 1898732717895963155960377, 1011844196551535741726366525322443 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also the row products of triangle A077316. Note that a(3) = 1729 is known as the Hardy-Ramanujan number. LINKS Nathaniel Johnston, Table of n, a(n) for n = 1..100 EXAMPLE a(1) = 2 a(2) = 3*5 = 15 a(3) = 7*13*19 = 1729 a(4) = 5*13*17*29 = 32045 a(5) = 11*31*41*61*71 = 60551711 a(6) = 7*13*19*31*37*43 = 85276009 MAPLE Tj := proc(n, k) option remember: local j, p: if(k=0)then return 0:fi: for j from procname(n, k-1)+1 do if(isprime(n*j+1))then return j: fi: od: end: A193869 := proc(n) return mul(n*Tj(n, k)+1, k=1..n): end: seq(A193869(n), n=1..15); # Nathaniel Johnston, Sep 02 2011 CROSSREFS Cf. A001235, A077316, A092609, A121940, A154729. Sequence in context: A068409 A359849 A096232 * A320768 A337799 A064171 Adjacent sequences: A193866 A193867 A193868 * A193870 A193871 A193872 KEYWORD nonn AUTHOR Omar E. Pol, Sep 01 2011 EXTENSIONS a(7)-a(14) from Nathaniel Johnston, Sep 02 2011 STATUS approved

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Last modified July 13 08:08 EDT 2024. Contains 374274 sequences. (Running on oeis4.)