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A179402 Numbers n such that all x^4 mod n are nonprimes. 1
1, 2, 3, 4, 5, 8, 12, 15, 16, 24, 28, 30, 40, 48, 56, 60, 72, 80, 85, 88, 96, 104, 105, 112, 120, 140, 145, 160, 168, 232, 240, 255, 265, 280, 312, 408, 420, 520, 624, 680, 760, 840, 1040, 1320, 1360, 1848, 1904, 4080 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A065428 is a subsequence.

No more such numbers up to 10^6.

Observe that many of these numbers are of the form k^2-1. Why?

LINKS

Table of n, a(n) for n=1..48.

PROG

(PARI) for(n=1, 10^6, q=1; for(x=1, n-1, if(isprime(component(Mod(x, n)^4, 2)), q=0; break())); if(q, print1(n, ", ")));

(PARI) {a(n) = my(c, m); if(n<=1, n==1, c=1; m=1; while( c<n, m++; c += prod(x=1, m-1, !isprime( lift( Mod(x, m)^4 ) ) ) ); m)}; /* Michael Somos, Jan 07 2011 */

CROSSREFS

A065428 (x^2 mod n).

Sequence in context: A053021 A122700 A048486 * A065428 A059747 A254328

Adjacent sequences:  A179399 A179400 A179401 * A179403 A179404 A179405

KEYWORD

nonn

AUTHOR

Joerg Arndt, Jan 07 2011

STATUS

approved

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Last modified September 23 01:32 EDT 2020. Contains 337291 sequences. (Running on oeis4.)