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Primes which set a new record for length of Pratt certificate.
3

%I #12 Sep 05 2024 05:06:30

%S 2,3,7,23,43,139,283,659,1319,5179,9227,23159,55399,148439,366683,

%T 793439,1953839,4875119,9750239,27353747,71815607,192287243,430893643

%N Primes which set a new record for length of Pratt certificate.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PrattCertificate.html">Pratt Certificate</a>.

%t a[1] = 1; a[n_] := a[n] = 1 + Plus @@ (a@ PrimePi@ # & /@ First /@ FactorInteger[ Prime@ n - 1]); t = Table[ 0, {25}]; k = 2; While[k < 23420001, b = a[k]/2; If[b < 1001 && t[[b]] == 0, t[[b]] = Prime@ k; Print[{b, Prime@ k }]]; k++]; t

%Y Cf. A037202.

%K nonn,more

%O 1,1

%A _David W. Wilson_