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A131626 Prime subsequences in the evaluation of the first derivatives of quadratic equations with positive successive prime coefficients. 0
7, 11, 17, 11, 17, 19, 29, 47, 67, 101, 23, 31, 47, 43, 47, 71, 59, 89, 67, 101, 167, 71, 107, 79, 83, 103, 107, 127, 191, 317, 131, 197, 139, 151, 227, 163, 167, 251, 179, 269, 191, 199, 211, 317, 223, 227, 239, 359, 251, 263, 271, 283, 307, 461, 311, 467, 331 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: The number of primes in a row for f'(x,p) = 2*prime(p)*x + prime(p+1) is finite.

LINKS

Table of n, a(n) for n=1..57.

FORMULA

Define prime(p) = the p-th prime number. The equation f(x,p) = prime(p)x^2 + prime(p+1)x + prime(p+2) is differentiated to get f'(x,p) = 2prime(p)x + prime(p+1). Then f'(x,p) is evaluated at p=1,2,.. for each x =1,2,.. until f'(x,p) is not prime at which point x is incremented and p=1,2,..

EXAMPLE

For x = 4 we have 2*prime(p)*x + prime(p+1) =

2*2*4+3 = 19 prime,

2*3*4+5 = 29 prime,

2*5*4+7 = 47 prime,

2*7*4+11 = 67 prime,

2*11*4+13 = 101 prime,

2*13*4+17 = 121 not prime.

So the subsequence 19,29,47,67,101 is in the sequence beginning in the 6th position.

PROG

(PARI) g(n) = { local(x, y, p); for(x=0, n, for(p=1, n, y=2*prime(p)*x+prime(p+1); if(isprime(y), print1(y", "), break) ) ) }

CROSSREFS

Sequence in context: A129188 A022950 A293343 * A086762 A296305 A076045

Adjacent sequences:  A131623 A131624 A131625 * A131627 A131628 A131629

KEYWORD

nonn

AUTHOR

Cino Hilliard, Sep 03 2007

STATUS

approved

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Last modified April 2 23:47 EDT 2020. Contains 333194 sequences. (Running on oeis4.)