A359490 Primes p followed by two or more 2-pseudoprimes (A001567) before the next prime.

4363, 13729, 31607, 6973007, 208969199

Offset

1,1

Comments

Is this sequence infinite? Is there a prime followed by three pseudoprimes before the next prime? I believe heuristics suggest "no" to both.

From Amiram Eldar, Mar 12 2023: (Start)

The primes preceding the terms of A335326.

There are no more terms below 2^64. (End)

Links

Table of n, a(n) for n=1..5.

Example

a(n): pseudoprimes following a(n)
4363: 4369, 4371
13729: 13741, 13747
31607: 31609, 31621
6973007: 6973057, 6973063
208969199: 208969201, 208969223

Prog

(PARI) prp(n, a=2)=Mod(a, n)^(n-1)==1
list(lim)=my(v=List(), p=3); forprime(q=5, lim, my(s=0); forstep(k=p+2, q-2, 2, if(prp(k) && s++>1, listput(v, p))); p=q); Vec(v)

Crossrefs

Cf. A001567, A335326.

Sequence in context: A164517 A125825 A031564 * A347603 A217345 A140937

Adjacent sequences: A359487 A359488 A359489 * A359491 A359492 A359493

Keyword

nonn,more

Author

Charles R Greathouse IV, Mar 07 2023

Status

approved