This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A055211 Lesser Fortunate numbers. 19
 3, 7, 11, 13, 17, 29, 23, 43, 41, 73, 59, 47, 89, 67, 73, 107, 89, 101, 127, 97, 83, 89, 97, 251, 131, 113, 151, 263, 251, 223, 179, 389, 281, 151, 197, 173, 239, 233, 191, 223, 223, 293, 593, 293, 457, 227, 311, 373, 257, 307, 313, 607, 347, 317, 307, 677, 467 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS a(1) is not defined. The first 1000 terms are all prime and it is conjectured that all terms are primes. a(n) is the smallest m such that m > 1 and A002110(n) - m is prime. For n > 2, a(n) must be greater than prime(n+1) - 1. - Farideh Firoozbakht, Aug 20 2003 Lim_{N->inf} (Sum_{n=2..N} a(n)) / (Sum_{n=2..N} prime(n)) = Pi/2; floor (a(n) / prime(n)) is always < 8. - Pierre CAMI, Aug 19 2017 LINKS Pierre CAMI, Table of n, a(n) for n=2..2000 C. Banderier, Conjecture checked for n<1000 [It has been reported that this data contains errors] Pierre CAMI, PFGW Script FORMULA a(n) = 1 + the difference between the n-th Primorial less one and the previous prime. EXAMPLE a(3) = 7 since 2*3*5 = 30, 30-1 = 29, previous prime is 23, 30-23 = 7. MAPLE for n from 2 to 60 do printf(`%d, `, product(ithprime(j), j=1..n) - prevprime(product(ithprime(j), j=1..n)-1)) od: MATHEMATICA PrevPrime[ n_Integer ] := Module[ {k = n - 1}, While[ ! PrimeQ[ k ], k-- ]; k ]; Primorial[ n_Integer ] := Module[ {k = Product[ Prime[ j ], {j, 1, n} ]}, k ]; LF[ n_Integer ] := (p = Primorial[ n ] - 1; q = PrevPrime[ p ]; p - q + 1); Table[ LF[ n ], {n, 2, 60} ] a[2]=3; a[n_] := (For[m=(Prime[n+1]+1)/2, !PrimeQ[Product[Prime[k], {k, n}] - 2m+1], m++ ]; 2m-1); Table[a[n], {n, 2, 60}] CROSSREFS Cf. A002110, A005235. Sequence in context: A020574 A020618 A184865 * A183176 A045417 A260379 Adjacent sequences:  A055208 A055209 A055210 * A055212 A055213 A055214 KEYWORD nonn AUTHOR Robert G. Wilson v, Jul 04 2000 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 10 20:55 EST 2018. Contains 318049 sequences. (Running on oeis4.)