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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

Table of n, a(n) for n=1..21.

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.)