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 A129472 Primes p of Erdos-Selfridge class 4+ with largest prime factor of p+1 not of class 3+. 3

%I

%S 3181,4513,4957,6067,7177,8731,9397,10433,13171,14947,15761,17389,

%T 19387,19609,22051,22273,22453,22717,23531,23753,24197,26161,27823,

%U 28711,37369,37591,38183,38923,39293,40993,41143,42697,43067,44621,44843

%N Primes p of Erdos-Selfridge class 4+ with largest prime factor of p+1 not of class 3+.

%C See A129470

%e a(1) = 3181 = -1+2*37*43 is a prime of class 4+ since 37 is of class 3+, but the largest divisor of 3181+1 is 43 which is only of class 2+.

%o (PARI) class(n,s=1)={n=factor(n+s)[,1];if(n[ #n]<=3,1,for(i=2,#n,n[1]=max(class(n[i],s)+1,n[1]));n[1])}; A129472(n=100,p=1,a=[])={ local(f); while( #a<n, until( f[ #f] > 3 & 3 > class(f[ #f]), f=factor(1+p=nextprime(p+1))[,1]); forstep( i=#f-1,2,-1, if( 4 < f[1] = max( f[1],1+class( f[i] )), next(2))); if( f[1] == 4, a=concat(a,p); /*print(#a," ",p)*/)); a}

%Y Subsequence of A129470; see also A129471, A129473, A129477-A129478, A129469, A005113, A005105-A005107.

%K easy,nonn

%O 1,1

%A _M. F. Hasler_, Apr 17 2007

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Last modified June 16 10:03 EDT 2019. Contains 324152 sequences. (Running on oeis4.)