

A071580


Smallest prime of the form k*a(n1)*a(n2)*...*a(1)+1.


4




OFFSET

1,1


COMMENTS

The former definition was "Smallest prime == 1 mod (a(n1)*a(n2)*...*a(1)) for n>=2 with a(1)=2."
a(6) through a(13), with digit lengths 8, 16, 32, 63, 127, 253, 507 and 1012, respectively, have been certified prime with Primo.


LINKS

Joerg Arndt, Table of n, a(n) for n = 1..13
Mersenne Forum, A071580


MAPLE

P:= 1:
for n from 1 to 13 do
for k from 1 do
if isprime(k*P+1) then
A[n]:= k*P+1;
P:= P * A[n];
break
fi
od
od:
seq(A[i], i=1..13); # Robert Israel, May 19 2015


MATHEMATICA

sp[{p_, a_}]:=Module[{k=1}, While[!PrimeQ[k*p+1], k++]; {p(p*k+1), p*k+1}]; NestList[sp, {2, 2}, 10][[All, 2]] (* Harvey P. Dale, Mar 04 2019 *)


PROG

(PARI) terms=13; v=vector(terms); p=2; v[1]=p; for(n=2, terms, q=p+1; while(!isprime(q), q=q+p); v[n]=q; p=p*q); v


CROSSREFS

Cf. A061092, A258081.
Sequence in context: A129871 A075442 A082993 * A267507 A344561 A014546
Adjacent sequences: A071577 A071578 A071579 * A071581 A071582 A071583


KEYWORD

nonn


AUTHOR

Rick L. Shepherd, May 31 2002


EXTENSIONS

Definition reworded by Andrew R. Booker, May 19 2015


STATUS

approved



