A129473 Primes p of Erdos-Selfridge class 5+ with largest prime factor of p+1 not of class 4+.

15913, 18541, 22921, 36353, 47741, 49201, 52267, 55333, 60589, 64969, 66137, 66721, 69203, 72707, 73291, 74167, 75773, 78401, 79861, 80737, 82051, 84533, 90227, 90373, 95191, 95483, 95629, 97673, 99133, 101323, 103951, 104681, 104827

Offset: 1

Author

M. F. Hasler, Apr 17 2007

Keywords

• easy
• nonn

Comments

See A129470

Examples

			a(1) = 15913 = -1+2*73*109 is a prime of class 5+ since 73 is of class 4+, but the largest divisor of 15913+1 is 109 which is only of class 2+.
		

Crossrefs

Subsequence of A129470; see also A129471-A129472, A129477-A129478, A129469, A005113, A005105-A005108, A081633.

Programs

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])}; A129473(n=100,p=1,a=[])={ local(f); while( #a 3 & 4 > class(f[ #f]), f=factor(1+p=nextprime(p+1))[,1]); forstep( i=#f-1,2,-1, if( 5 < f[1] = max( f[1],1+class( f[i] )), next(2))); if( f[1] == 5, a=concat(a,p); /*print(#a," ",p)*/)); a}