A145991 Final prime in a run of more than 1 consecutive primes == 1 (mod 4).

17, 41, 101, 113, 197, 233, 281, 317, 353, 409, 461, 521, 617, 677, 709, 773, 809, 857, 881, 941, 1013, 1097, 1117, 1217, 1249, 1301, 1381, 1433, 1493, 1553, 1601, 1613, 1657, 1697, 1721, 1741, 1801, 1877, 1901, 1949, 1997, 2081, 2129, 2141, 2161, 2237

Offset: 1

Author

Enoch Haga, Oct 26 2008

Keywords

• easy
• nonn

Examples

			a(1)=17 because this sequence includes consecutive runs of any length and this ending term > 1 in a run of 2 (comprising 13 and 17) is 17.
		

References

• Enoch Haga, Exploring Primes on Your PC and the Internet, 1994-2007. Pp. 30-31. ISBN 978-1-885794-24-6

Crossrefs

Cf. A055623, A054624, A145986, A145988- A145994

Programs

UBASIC

10 'cluster primes
20 C=1
30 input "end #";L
40 for N=3 to L step 2
50 S=int(sqrt(N))
60 for A=3 to S step 2
70 B=N/A
80 if int(B)*A=N then cancel for:goto 170
90 next A
100 C=C+1
110 E=N/4:E=int(E):R=N-(4*E)
120 if R=1 then print N;:C1=C1+1:T1=T1+1:print T1
130 if R=3 then T1=0
140 if R=3 then print " ";N;:C3=C3+1:T2=T2+1:print T2
150 if R=1 then T2=0
160 if T1>10 or T2>10 then stop
170 next
180 print "Total primes=";C;:print "Type A";C1;"Type B";C3