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A130097 Primes prime(n) such that at least one of the two numbers (prime(n+2)^2-prime(n)^2)/2 - 1 and (prime(n+2)^2-prime(n)^2)/2 + 1 is not prime. 1
3, 5, 11, 13, 17, 23, 29, 31, 41, 43, 47, 53, 59, 73, 79, 83, 89, 101, 103, 109, 113, 131, 137, 139, 149, 151, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

a(1)=3 because (7^2 - 3^2)/2 - 1 = 19 and (7^2 - 3^2)/2 + 1 = 21 (21 is not prime),

a(2)=5 because (11^2 - 5^2)/2 - 1 = 47 and (11^2 - 5^2)/2 + 1 = 49 (49 is not prime),

a(3)=11 because (17^2 - 11^2)/2 - 1 = 83 and (17^2 - 11^2)/2 + 1 = 85 (85 is not prime), ...

MAPLE

ts_p2_20:=proc(n) local a, b, i, ans; ans := [ ]: for i from 2 to n do a := (ithprime(i+2)^(2)-ithprime(i)^(2))/2-1: b := (ithprime(i+2)^(2)-ithprime(i)^(2))/2+1: if not (isprime(a)=true and isprime(b)=true) then ans := [ op(ans), ithprime(i) ]: fi od; RETURN(ans) end: ts_p2_20(300);

CROSSREFS

Cf. A130761.

Sequence in context: A178942 A045404 A152460 * A020612 A072539 A062391

Adjacent sequences:  A130094 A130095 A130096 * A130098 A130099 A130100

KEYWORD

nonn

AUTHOR

Jani Melik, Aug 01 2007

STATUS

approved

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Last modified May 16 19:46 EDT 2021. Contains 343951 sequences. (Running on oeis4.)