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 A129470 Primes p such that the largest prime factor of p+1 has Erdos-Selfridge class+ < N-1 if p is of class N+. 7
 883, 1747, 2417, 2621, 3181, 3301, 3533, 3571, 3691, 3853, 4027, 4133, 4513, 4783, 4861, 4957, 5303, 5381, 5393, 5563, 5641, 5821, 6067, 6577, 6991, 7177, 7253, 7331, 8059, 8093, 8377, 8731, 8839, 8929, 8969, 9221, 9281, 9397, 9613, 9931 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS In practice the class+ of a prime p is most often given by 1 + the class of the largest prime factor of p+1; elements of this sequence are counter-examples to this "rule". Elements of this sequence are at least of class 3+, since primes of class 1+ and 2+ have all prime factors of p+1 of class 1+. Elements a(k) of this sequence are >= -1+2*A005113[N-1]*nextprime(A005113[N-1]), where N is the class of a(k). LINKS EXAMPLE a(3) = 883 = -1+2*13*17 is a prime of class 3+ since 13 is of class 2+, but the largest divisor of 883+1 is 17 which is only of class 1+. PROG (PARI) class(n, s=1)={n=factor(n+s)[, 1]; if(n[ #n]<=3, 1, for(i=2, #n, n=max(class(n[i], s)+1, n)); n)}; A129470(n=100, p=1, a=[])={ local(f); while( #a 3, f=factor(1+p=nextprime(p+1))[, 1]); forstep( i=#f, 2, -1, f[i]=class( f[i] ); if( f[i] > f[ #f], a=concat(a, p); /*print(#a, " ", p); */ break))); a} CROSSREFS Cf. A129471-A129473, A129477-A129478, A129469, A005113, A005105-A005108, A081633-A081639, A084071, A090468, A129474-A129475. Sequence in context: A207054 A096992 A260926 * A129471 A023312 A129469 Adjacent sequences:  A129467 A129468 A129469 * A129471 A129472 A129473 KEYWORD easy,nonn AUTHOR M. F. Hasler, Apr 16 2007 STATUS approved

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Last modified June 24 10:00 EDT 2019. Contains 324323 sequences. (Running on oeis4.)