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A145173 Least a(n) such that p(n)#*(p(n)#-a(n))-1 is prime with p(i)#=i-th primorial. 2
0, 1, 2, 1, 2, 4, 2, 1, 4, 9, 1, 2, 14, 2, 3, 9, 2, 9, 24, 1, 25, 1, 7, 8, 2, 52, 14, 13, 42, 7, 22, 8, 5, 20, 36, 9, 8, 10, 36, 56, 2, 14, 42, 7, 2, 128, 159, 45, 49, 1, 16, 69, 211, 80, 19, 13, 3, 12, 25, 21, 106, 32, 39, 26, 21, 23, 5, 22, 66, 43, 45, 139, 350, 38, 26, 145, 19, 142 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

As n increases the sum a(n) for i=1 to n tends to n*(n+1)/2.

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..704

EXAMPLE

2*(2-0-1=3 prime so a(1)=0 2*3*(2*3-1)-1=29 prime so a(2)=1 2*3*5*(2*3*5-2)-1=839 prime so a(3)=2

PROG

(PARI) { allocatemem(932245000); default(primelimit, 4294965247); n=0; p=1; q=1; until (0, n=n+1; p=nextprime(p+1); q=q*p; for (a=0, 1000000000, r=q*(q-a)-1; if (isprime(r), print(n, " ", a); write("b145173.txt", n, " ", a); break; ); ) ) } [From Harry J. Smith, Jan 14 2009]

CROSSREFS

Cf. A144946, A144947

Sequence in context: A225081 A097082 A281729 * A270594 A270706 A082793

Adjacent sequences:  A145170 A145171 A145172 * A145174 A145175 A145176

KEYWORD

nonn

AUTHOR

Pierre CAMI, Oct 03 2008

EXTENSIONS

Corrected by several correspondents, Jan 14 2009

STATUS

approved

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Last modified March 29 15:31 EDT 2017. Contains 284273 sequences.