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

1,1

Comments

See A129470

Links

Table of n, a(n) for n=1..33.

Example

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+.

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])}; A129473(n=100, p=1, a=[])={ local(f); while( #a<n, until( f[ #f] > 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}

Crossrefs

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

Sequence in context: A174596 A237071 A251848 * A372550 A237681 A218642

Adjacent sequences: A129470 A129471 A129472 * A129474 A129475 A129476

Keyword

easy,nonn

Author

M. F. Hasler, Apr 17 2007

Status

approved