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 A264886 Integers n such that A061720(n-1) + 1 or A061720(n-1) - 1 is prime. 0
 1, 2, 3, 4, 5, 8, 9, 15, 25, 36, 57, 80, 81, 133, 225, 281, 282, 288, 343, 632, 653 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Integers n such that A002110(n) - A002110(n-1) + 1 or A002110(n) - A002110(n-1) - 1  is prime. Are there any other squares in sequence? LINKS EXAMPLE a(3) = 3 because 2*3*5 - 2*3 - 1 = 23 is prime. a(6) = 8 because 2*3*5*7*11*13*17*19 - 2*3*5*7*11*13*17 + 1 = 9189181 is prime. MATHEMATICA t = Differences[FoldList[Times, 1, Prime@ Range@ 1200]]; Select[Range@ 360, Or[PrimeQ[t[[# - 1]] + 1], PrimeQ[t[[# - 1]] - 1]] &] - 1 (* Michael De Vlieger, Nov 28 2015, after Alonso del Arte at A061720 *) PROG (PARI) a(n) = prod(k=1, n, prime(k)); for(n=0, 1e3, if(ispseudoprime(a(n)-a(n-1)-1) || ispseudoprime(a(n)-a(n-1)+1), print1(n, ", "))) CROSSREFS Cf. A002110, A061720. Sequence in context: A054168 A301464 A085152 * A287117 A286431 A015931 Adjacent sequences:  A264883 A264884 A264885 * A264887 A264888 A264889 KEYWORD nonn,more AUTHOR Altug Alkan, Nov 27 2015 STATUS approved

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Last modified May 26 15:17 EDT 2019. Contains 323596 sequences. (Running on oeis4.)