A129471 Primes p of Erdos-Selfridge class 3+ with largest prime factor of p+1 not of class 2+.

883, 1747, 2417, 2621, 3301, 3533, 3571, 3691, 3853, 4027, 4133, 4783, 4861, 5303, 5381, 5393, 5563, 5641, 5821, 6577, 6991, 7253, 7331, 8059, 8093, 8377, 8839, 8929, 8969, 9221, 9281, 9613, 9931, 10069, 10477, 10487, 10601, 10607, 10903, 11491

Offset

1,1

Comments

See A129470

Links

Table of n, a(n) for n=1..40.

Example

a(1) = 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[1]=max(class(n[i], s)+1, n[1])); n[1])}; A129471(n=100, p=1, a=[])={ local(f); while( #a<n, until( f[ #f] > 3 & 2 > class(f[ #f]), f=factor(1+p=nextprime(p+1))[, 1]); forstep( i=#f-1, 2, -1, if( 3 < f[1] = max( f[1], 1+class( f[i] )), next(2))); if( f[1] == 3, a=concat(a, p); /*print(#a, " ", p)*/)); a}

Crossrefs

Subsequence of A129470; see also A129472-A129473, A129477-A129478, A129469, A005113, A005105-A005107.

Sequence in context: A096992 A260926 A129470 * A023312 A129469 A206794

Adjacent sequences: A129468 A129469 A129470 * A129472 A129473 A129474

Keyword

easy,nonn

Author

M. F. Hasler, Apr 17 2007

Status

approved