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 A125191 Primes of the form k# + (k+1)# +- 1, where k# = A002110(k) = primorial(k). 2
 2, 7, 37, 239, 241, 2521, 32341, 540539, 540541, 232792559, 232792561, 207030183359, 311671001662019, 41287621429375723111588738861, 5801527386969669153864265802424086050777441586253956297278498679 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Prime numbers of the form (prime(k+1) + 1)*k# +- 1. LINKS Table of n, a(n) for n=1..15. EXAMPLE Let k = 1; then 1#+2# = 2+6 = 8, 8-1 = 7 is prime (hence a term of the sequence) but 8+1 = 9 is nonprime. Let k = 3; then 3#+4# = 30+210 = 240, 240-1 = 239 is prime and 240+1 = 241 is also prime, so both are terms. MAPLE A002110 := 1 : A000040 := 2 : for n from 1 to 38 do if isprime(A002110*(1+A000040)-1) then printf("%d, ", A002110*(1+A000040)-1) ; fi ; if isprime(A002110*(1+A000040)+1) then printf("%d, ", A002110*(1+A000040)+1) ; fi ; A002110 := A002110*A000040 : A000040 := nextprime(A000040) : od : # R. J. Mathar, Jan 26 2007 PROG (PARI) {m=37; for(n=0, m, p=primorial(n)+primorial(n+1); if(isprime(a=p-1), print1(a, ", ")); if(isprime(a=p+1), print1(a, ", ")))} \\ Klaus Brockhaus, Jan 25 2007 (PARI) genit(maxx)={arr=List(); for(n=0, maxx, p=factorback(primes(n))+factorback(primes(n+1)); if(ispseudoprime(p-1), listput(arr, p-1)); if(ispseudoprime(p+1), listput(arr, p+1))); arr} \\ Bill McEachen, Jun 21 2021 (from David A. Corneth's code at A002110) CROSSREFS Cf. A002110 (primorial numbers), A006862 (Euclid numbers), A057588 (Kummer numbers). Sequence in context: A245902 A063766 A020040 * A300559 A302859 A338182 Adjacent sequences: A125188 A125189 A125190 * A125192 A125193 A125194 KEYWORD nonn AUTHOR Tomas Xordan, Jan 12 2007 EXTENSIONS Edited, corrected and extended by Klaus Brockhaus and R. J. Mathar, Jan 25 2007 STATUS approved

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Last modified August 8 18:48 EDT 2024. Contains 375023 sequences. (Running on oeis4.)