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A321616 Primes p = k^2 + (k-1)^2 such that k^p - (k-1)^p is prime. 0
5, 61, 113, 1741 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: generally, these are primes p = a^2 + b^2 with a > b > 0 such that (a^p - b^p)/(a-b) is prime, so must be a-b = 1. It seems that there are no primes (a^q + b^q)/(a+b) for primes q = a^2 + b^2 > 5. Especially, there are probably no primes q = m^2 + 1 > 5 such that (m^q - 1)/(m-1) is prime or (m^q + 1)/(m+1) is prime. How to prove it?

No more terms up to the prime 19801 = 100^2 + 99^2. - Amiram Eldar, Nov 15 2018

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

The prime 5 = 2^2 + 1^2 and 2^5 - 1^5 = 31 is prime.

We have 61 = 6^2 + 5^2, 113 = 8^2 + 7^2, 1741 = 30^2 + 29^2.

MATHEMATICA

f[k_]:=k^2 + (k-1)^2 ; seqQ[k_]:=Module[{p=f[k]}, PrimeQ[p] && PrimeQ[k^p - (k-1)^p ]]; f[Select[Range[30], seqQ]] (* Amiram Eldar, Nov 15 2018 *)

PROG

(PARI) lista(nn) = {for (k=1, nn, if (isprime(p=k^2 + (k-1)^2) && isprime(k^p - (k-1)^p), print1(p, ", ")); ); } \\ Michel Marcus, Nov 18 2018

CROSSREFS

Cf. A002144, A121091.

Subsequence of A027862.

Sequence in context: A139915 A174053 A107191 * A182352 A142643 A201848

Adjacent sequences:  A321613 A321614 A321615 * A321617 A321618 A321619

KEYWORD

nonn,more

AUTHOR

Thomas Ordowski, Nov 15 2018

STATUS

approved

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Last modified February 25 21:55 EST 2020. Contains 332264 sequences. (Running on oeis4.)