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A129472 Primes p of Erdos-Selfridge class 4+ with largest prime factor of p+1 not of class 3+. 4
3181, 4513, 4957, 6067, 7177, 8731, 9397, 10433, 13171, 14947, 15761, 17389, 19387, 19609, 22051, 22273, 22453, 22717, 23531, 23753, 24197, 26161, 27823, 28711, 37369, 37591, 38183, 38923, 39293, 40993, 41143, 42697, 43067, 44621, 44843 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
LINKS
EXAMPLE
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+.
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])}; 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}
CROSSREFS
Sequence in context: A155484 A345599 A345858 * A023309 A023337 A236131
KEYWORD
easy,nonn
AUTHOR
M. F. Hasler, Apr 17 2007
STATUS
approved

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Last modified April 23 22:36 EDT 2024. Contains 371917 sequences. (Running on oeis4.)