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%I A091878 #7 Mar 31 2012 14:11:24
%S A091878 4920,801528,1484280,5351640,7257720,7647360,12168912,12302472,
%T A091878 15540360,17348520,21623160,25639320,27285048,27462840,27470352,
%U A091878 34714680,35684040,38466288,48449640,49936152,51272760,54037368,60948888
%N A091878 a(n) can be expressed as the difference of the squares of consecutive primes in just four distinct ways.
%e A091878 4920=211^2-199^2=251^2-241^2=617^2-613^2=1231^2-1229^2
%o A091878 (C) #define NMAX 200000000 #include <stdlib.h> #include <stdio.h> #include <limits.h> int isprime(const int n) { for(int i=2 ; i*i <= n ; i++) if( n % i == 0) return(0) ; return 1 ; } int main(int argc, char *argv[]) { short * n= (short*)calloc(NMAX,sizeof(short)) ; int wm=0; for(int p=2 ; ; ) { int np=p+1 ; while( !isprime(np) ) np++ ; if(np<0) break ; if ( p+np < INT_MAX/(np-p) ) { const int i=(p+np)*(np-p) ; const int nw= p+np ; if( i < NMAX ) n[i]++ ; for(int j=wm ; j < nw ; j++) if ( n[j] == 4) printf("%d ",j) ; wm=nw ; } p=np ; if( p > INT_MAX-np ) break ; } free(n) ; } - _R. J. Mathar_, Oct 05 2006
%Y A091878 Cf. A078667, A090783, A090784, A090785.
%K A091878 nonn
%O A091878 1,1
%A A091878 _Ray G. Opao_ and _Ray Chandler_, Feb 11 2004
%E A091878 More terms from _R. J. Mathar_, Oct 05 2006

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