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A175663 Maximal run length of primes of the form n, n+2, n+2*3, n+2*3*5,.. 3
0, 1, 2, 0, 3, 0, 1, 0, 0, 0, 4, 0, 1, 0, 0, 0, 5, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 9, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 6, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
a(n) <= A175682(n). - Antti Karttunen, Jan 03 2019
EXAMPLE
a(107)=8 because 107=prime, 107+2=109=prime, 107+2*3=113=prime, 107+2*3*5=137=prime, 107+2*3*5*7=317=prime, 107+2*3*5*7*11=2417=prime, 107+2*3*5*7*11*13=30137=prime, 107+2*3*5*7*11*13*17=510617=prime.
MAPLE
A002110 := proc(n) option remember; mul(ithprime(i), i=1..n) ; end proc:
A175663 := proc(n) if isprime(n) then for p from 1 do if not isprime(n+A002110(p)) then return p ; end if; end do: else return 0 ; end if; end proc:
seq(A175663(n), n=1..120) ; # R. J. Mathar, Aug 07 2010
MATHEMATICA
Array[If[PrimeQ@ #, Block[{s = {1}}, While[PrimeQ[# + Times @@ Prime@ s], AppendTo[s, s[[-1]] + 1]]; Last@ s], 0] &, 105] (* Michael De Vlieger, Jan 03 2019 *)
PROG
(PARI) A175663(n) = if(!isprime(n), 0, my(pr=2); for(k=1, oo, if(!isprime(pr+n), return(k)); pr *= prime(1+k))); \\ Antti Karttunen, Jan 03 2019
CROSSREFS
Cf. A006512 (greater of twin primes), A175612 (list of twin semiprimes), A175648 (lesser of twin semiprimes).
Cf. also A175682.
Sequence in context: A291044 A113290 A078442 * A240672 A352288 A243016
KEYWORD
nonn
AUTHOR
Vladislav-Stepan Malakovsky & Juri-Stepan Gerasimov, Aug 04 2010
STATUS
approved

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Last modified May 23 05:11 EDT 2024. Contains 372758 sequences. (Running on oeis4.)