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A208455 Primes p such that (p+k)/(k+1) is a prime number for k=1,...,5. 3
5516281, 16831081, 18164161, 29743561, 51755761, 148057561, 153742681, 158918761, 175472641, 189614881, 212808961, 297279361, 298965241, 322030801, 467313841, 527428441, 661686481, 668745001, 751524481, 808214401 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A071368 consisting of elements ending in the digit 1. (Proof: Let n=10k+1, {n,n+1,...,n+5}={P1,2*P2,...,6*P6} with P1,...,P6 prime. Obviously n+4=10k+5=5*P5. Since n+1==n+5 (mod 4), none of these two can be 4*P4. Thus, n+3=4*P4, whence n==P4 (mod 3) and n cannot be 3*P3. Therefore n=P1 and n+2=3*P3. Then n+5 is an even multiple of 3, n+5=6*P6, and n+1=2*P2 is the only remaining choice.)

Also: The subsequence of p in A204592 such that (p+5)/6 is a prime number. All terms are congruent to 1 modulo 2520 = A003418(9) = 7!/2 = 5*7*8*9.

LINKS

M. F. Hasler, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[1, 810*10^6, 2520], PrimeQ[#]&&AllTrue[Table[(#+k)/(k+1), {k, 5}], PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Jul 21 2015 *)

PROG

(PARI) {my(p=1); until(, isprime(p+=2520) | next; for(j=2, 6, isprime(p\j+1)|next(2)); print1(p", "))}

(PARI) is_A208455(p, c=6)={ isprime(p) || return; for(j=2, c, isprime(p\j+1) || return); 1 }

CROSSREFS

Cf. A093553. A207825 is a subsequence.

Sequence in context: A283652 A206176 A205430 * A207825 A204802 A227931

Adjacent sequences:  A208452 A208453 A208454 * A208456 A208457 A208458

KEYWORD

nonn

AUTHOR

M. F. Hasler, Feb 27 2012

EXTENSIONS

Value of A208455(1000) = 147435621481 = 58506199*2520+1 confirmed by Zak Seidov.

STATUS

approved

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Last modified July 29 22:26 EDT 2021. Contains 346346 sequences. (Running on oeis4.)