A056994 -id:A056994 - cp's OEIS frontend

A250176 Numbers n such that Phi_20(n) is prime, where Phi is the cyclotomic polynomial.

4, 9, 11, 16, 19, 26, 34, 45, 54, 70, 86, 91, 96, 101, 105, 109, 110, 119, 120, 126, 129, 139, 141, 149, 171, 181, 190, 195, 215, 229, 260, 276, 299, 305, 309, 311, 314, 319, 334, 339, 369, 375, 414, 420, 425, 444, 470, 479, 485, 506, 519, 534, 540, 550

Offset: 1

Eric Chen, Dec 24 2014

nonn

G. C. Greubel, Table of n, a(n) for n = 1..10000

Cf. A008864 (1), A006093 (2), A002384 (3), A005574 (4), A049409 (5), A055494(6), A100330 (7), A000068 (8), A153439 (9), A246392 (10), A162862(11), A246397 (12), A217070 (13), A006314 (16), A217071 (17), A164989(18), A217072 (19), A217073 (23), A153440 (27), A217074 (29), A217075(31), A006313 (32), A097475 (36), A217076 (37), A217077 (41), A217078(43), A217079 (47), A217080 (53), A217081 (59), A217082 (61), A006315(64), A217083 (67), A217084 (71), A217085 (73), A217086 (79), A153441(81), A217087 (83), A217088 (89), A217089 (97), A006316 (128), A153442(243), A056994 (256), A056995 (512), A057465 (1024), A057002 (2048), A088361 (4096), A088362 (8192), A226528 (16384), A226529 (32768), A226530(65536).

Select[Range[600], PrimeQ[Cyclotomic[20, #]] &] (* Vincenzo Librandi, Jan 16 2015 *)

isok(n) = isprime(polcyclo(20, n)); \\ Michel Marcus, Sep 29 2015

More terms from Vincenzo Librandi, Jan 16 2015

A085299 a(n) is the smallest number x such that A085298[x]=n, or 0 if no such number exists.

Original entry on oeis.org

1, 8, 47, 18, 14, 89, 10, 9, 48, 16, 23, 17, 168, 268, 15, 661, 50, 380, 84, 116, 360, 245, 29, 144, 345, 227, 785, 261, 148, 235, 691, 658, 638, 40, 1023, 674, 1529, 210, 19, 81, 181, 428, 170, 1130, 2322, 406, 600, 373, 958, 217

Offset: 1

Labos Elemer, Jun 24 2003

			a(13) = 168 means that 13 is the smallest exponent such that reversed[p(168)^13] = reversed[997^13] = 776831144302925059735912605306533496169
is prime if read in this direction and 13th prime-power if read backwards.

Cf. A085298, A057708, A058993, A056994, A059695, A003459, A007500, A055387, A061461, A068652.

A087738 Square array: T(n,k) gives n-th number a such that a^(2^k)+1 is prime (a generalized Fermat).

Original entry on oeis.org

1, 2, 1, 4, 2, 1, 6, 4, 2, 1, 10, 6, 4, 2, 1, 12, 10, 6, 4, 2, 1, 16, 14, 16, 118, 44, 30, 1, 18, 16, 20, 132, 74, 54, 102, 1, 22, 20, 24, 140, 76, 96, 162, 120, 1, 28, 24, 28, 152, 94, 112, 274, 190, 278, 1, 30, 26, 34, 208, 156, 114, 300, 234, 614, 46, 1, 36, 36, 46, 240, 158

Offset: 0

Jeppe Stig Nielsen, Oct 01 2003

			{1}; {2,1}; {4,2,1}; ...
See the well-formed array on Gallot's page.

Harvey Dubner, J. Recr. Math., 18, 1986.

Yves Gallot, Generalized Fermat Prime Search.

Cf. A056993, A006093, A005574, A000068, A006314, A006313, A006315, A006316, A056994, A056995, A057465, A057002, A088361, A088362.

A217993 Smallest k such that k^(2^n) + 1 and (k+2)^(2^n) + 1 are both prime.

Original entry on oeis.org

2, 2, 2, 2, 74, 112, 2162, 63738, 13220, 54808, 3656570, 6992032, 125440, 103859114, 56414914, 87888966

Offset: 0

Michel Lagneau, Oct 17 2012

a(15)=87888966 but a(14) is unknown. - Jeppe Stig Nielsen, Mar 17 2018

The prime pair related to a(14) was found four days ago, and today double checking has proved that they are indeed the first occurrence for n=14. - Jeppe Stig Nielsen, May 02 2018

			a(0) = 2 because 2^1+1 = 3 and 4^1+1 = 5 are prime;
a(1) = 2 because 2^2+1 = 5  and 4^2+1 = 17 are prime;
a(2) = 2 because 2^4+1 = 17  and 4^4+1 = 257 are prime;
a(3) = 2 because  2^8+1 = 257 and 4^8+1 = 65537 are prime.

Cf. A006313, A006314, A006315, A006316, A056994, A056995, A057465, A057002, A088361, A088362, A118539.

for n from 0  to 5 do:ii:=0:for k from 2 by 2 to 10000 while(ii=0) do:if type(k^(2^n)+1,prime)=true and type((k+2)^(2^n)+1,prime)=true then ii:=1: printf ( "%d %d \n",n,k):else fi:od:od:

a(n) = A118539(n)-1. - Jeppe Stig Nielsen, Feb 27 2016

a(13) from Jeppe Stig Nielsen, Mar 17 2018

a(14) and a(15) from Jeppe Stig Nielsen, May 02 2018

A242557 Least number k such that n^128+k^128 is prime.

Original entry on oeis.org

1, 113, 106, 259, 304, 85, 212, 135, 158, 47, 62, 985, 84, 47, 518, 485, 178, 169, 106, 27, 88, 139, 632, 47, 44, 643, 20, 209, 606, 1529, 32, 31, 1094, 139, 754, 647, 38, 37, 262, 69, 94, 631, 90, 25, 38, 195, 10, 277, 232, 187, 554, 189, 10, 47, 216, 131, 1132, 173, 390

Offset: 1

Derek Orr, May 17 2014

nonn

If a(n) = 1, then n is in A056994.

Cf. A069003, A056994.

lnk[n_]:=Module[{c=n^128,k},k=If[EvenQ[c],1,2];While[!PrimeQ[c+ k^128],k = k+2];k]; Join[{1},Array[lnk,60,2]] (* Harvey P. Dale, Mar 17 2015 *)

a(n)=for(k=1,10^4,if(ispseudoprime(n^128+k^128),return(k)));
n=1;while(n<100,print(a(n));n+=1)

import sympy
from sympy import isprime
def a(n):
    for k in range(10**4):
        if isprime(n**128+k**128):
            return k
n = 1
while n < 100:
    print(a(n))
    n += 1

A244950 Least number k > n such that k^128 + n^128 is prime.

Original entry on oeis.org

120, 113, 106, 259, 304, 85, 212, 135, 158, 47, 62, 985, 84, 47, 518, 485, 178, 169, 106, 27, 88, 139, 632, 47, 44, 643, 194, 209, 606, 1529, 32, 113, 1094, 139, 754, 647, 38, 45, 262, 69, 94, 631, 90, 527, 326, 195, 54, 277, 232, 187, 554, 189, 78, 799, 216, 131, 1132, 173

Offset: 1

Derek Orr, Jul 08 2014

nonn

a(n) = n+1 iff n is in A215431.

			The n-value for which n^128 + 1 is prime (sequence A056994) is n = 120 (where n > 1 by definition). Thus a(1) = 120.

Jens Kruse Andersen, Table of n, a(n) for n = 1..1000

Cf. A158979, A089489, A242557.

lnk[n_]:=Module[{k=n+1,n128=n^128},While[!PrimeQ[n128+k^128],k++];k]; Array[lnk,60] (* Harvey P. Dale, Apr 22 2018 *)

a(n)=for(k=n+1,10^4,if(isprime(k^128+n^128),return(k)))
n=1;while(n<100,print1(a(n),", ");n++)

import sympy
from sympy import isprime
def a(n):
    for k in range(n+1,10**4):
        if isprime(k**128+n**128):
            return k
for n in range(1, 100):
    print(a(n), end=', ')

A272137 Primes of the form k^16 + 1.

Original entry on oeis.org

2, 65537, 197352587024076973231046657, 808551180810136214718004658177, 1238846438084943599707227160577, 37157429083410091685945089785857, 123025056645280288014028950372089857, 150838912030874130174020868290707457

Offset: 1

Jaroslav Krizek, May 08 2016

nonn

Corresponding values of k are in A006313.

Jaroslav Krizek, Table of n, a(n) for n = 1..100

Cf. Sequences of numbers n such that n^(2^k)+1 is a prime p for k = 1-13: A005574 (k=1), A000068 (k=2), A006314 (k=3), A006313 (k=4), A006315 (k=5), A006316 (k=6), A056994 (k=7), A056995 (k=8), A057465 (k=9), A057002 (k=10), A088361 (k=11), A088362 (k=12), A226528 (k=13).

Corresponding sequences of primes p of the form n^(2^k)+1 for k = 1-4: A002496 (k=1), A037896 (k=2), A258805 (k=3), A272137 (k=4).

[n^16 + 1: n in [1..700] | IsPrime(n^16 + 1)];

A272137:=n->`if`(isprime(n^16+1), n^16+1, NULL): seq(A272137(n), n=1..200); # Wesley Ivan Hurt, May 11 2016

A277967 Number of even numbers b with 0 < b < 2^n such that b^(2^n) + 1 is prime.

Original entry on oeis.org

0, 1, 2, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 0, 0, 1, 2, 3, 4, 1

Offset: 1

Jeppe Stig Nielsen, Nov 06 2016

The choice whether to take b < 2^n or b <= 2^n matters only for n=1 and n=2 unless there are more primes like 2^2+1 and 4^4+1 (see A121270).
Perfect squares b are allowed.
a(20) was determined after a lengthy computation by distributed project PrimeGrid, cf. A321323. - Jeppe Stig Nielsen, Jan 02 2019

			For n=18, we get b^262144 + 1 is prime for b=24518, 40734, 145310, 361658, 525094, ...; the first 3 of these b values are strictly below 262144, hence a(18)=3.
The corresponding primes are 2^4+1; 2^8+1, 4^8+1; 2^16+1; 30^32+1; 120^128+1; 46^512+1; etc.

Y. Gallot, Status of the smallest base values yielding Generalized Fermat primes.
PrimeGrid, GFN Prime Search Status and History.

Cf. A056993, A121270, A259835, A005574, A000068, A006314, A006313, A006315, A006316, A056994, A056995, A057465, A057002, A088361, A088362, A226528, A226529, A226530, A251597, A253854, A244150, A243959, A321323, etc.

Table[Count[Range[2, 2^n - 1, 2], b_ /; PrimeQ[b^(2^n) + 1]], {n, 9}] (* Michael De Vlieger, Nov 10 2016 *)

a(n)=sum(k=1,2^(n-1)-1,ispseudoprime((2*k)^2^n+1)) \\ slow, only probabilistic primality test

a(20) from Jeppe Stig Nielsen, Jan 02 2019

cp's OEIS Frontend

A250176 Numbers n such that Phi_20(n) is prime, where Phi is the cyclotomic polynomial.

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A085299 a(n) is the smallest number x such that A085298[x]=n, or 0 if no such number exists.

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A087738 Square array: T(n,k) gives n-th number a such that a^(2^k)+1 is prime (a generalized Fermat).

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A217993 Smallest k such that k^(2^n) + 1 and (k+2)^(2^n) + 1 are both prime.

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A242557 Least number k such that n^128+k^128 is prime.

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A244950 Least number k > n such that k^128 + n^128 is prime.

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A272137 Primes of the form k^16 + 1.

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Magma

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A277967 Number of even numbers b with 0 < b < 2^n such that b^(2^n) + 1 is prime.

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Mathematica

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