[seqfan] Re: A155882: Correct list(?)

[Richard Mathar]

zs> From seqfan-bounces at list.seqfan.eu Sat Jan 31 10:54:07 2009
zs> Date: Sat, 31 Jan 2009 01:30:38 -0800 (PST)
zs> From: zak seidov <zakseidov at yahoo.com>
zs> To: seqfaneu <seqfan at seqfan.eu>
zs> Subject: [seqfan]  A155882: Correct list(?)
zs> 
zs> Is this correct list of A155882?:
zs> 5, 11, 13, 17, 23, 31, 41, 47, 67, 71, 83, 109, 113, 131, 139, 149, 167, 193, 197, 233, 241, 251, 263, 271, 283, 317, 331, 347, 353, 373, 379, 401, 439, 443, 479, 487, 491, 503, 523, 541, 563, 571, 577, 587, 613, 619, 641, 727, 733, 761, 787, 809, 863, 877, 883, 887, 907, 919, 947, 991, 997, 1031, 1039, 1061, 1103, 1129, 1151, 1163, 1171, 1181, 1187, 1231, 1237, 1277, 1279, 1283, 1301, 1327, 1367, 1373, 1399, 1409, 1433, 1447, 1451, 1487, 1549, 1559, 1571, 1609, 1621, 1697, 1723, 1747, 1811, 1873, 1877, 1889, 1933
zs> 

My version differs from both the current A155882 and that
corrected one:

5, 7, 11, 13, 17, 19, 31, 47, 59, 61, 83, 97, 109, 131, 137, 139, 173, 193,
    211, 233, 239, 241, 257, 271, 277, 281, 283, 307, 389, 397, 409, 431, 433,
    457, 467, 491, 523, 563, 569, 571, 653, 661, 673, 701, 709, 733, 821, 823,
    859, 887, 911, 967, 983, 991, 997, 1019, 1021, 1063, 1109, 1117, 1153,
    1163, 1187, 1231, 1259, 1283, 1297, 1307, 1319, 1321, 1373, 1381, 1423,
    1427, 1429, 1453, 1481, 1483, 1531, 1559, 1571, 1597, 1613, 1619, 1621,
    1721, 1723, 1747, 1787, 1789, 1801, 1811, 1823, 1999, 2063, 2069, 2083,
    2129, 2131, 2179

At n=2, 7-2*2=3 is prime, so a(2)=7, not 11 as stated before.
n=3: 11-2*3=5, prime
n=4: 13-2*4=5, prime
n=5: 17-2*5=7, prime
n=6: 19-2*6=7, prime
n=7: 31-2*7=17, prime
etc

Maple program:

A155882 := proc(n) option remember;
        if n = 1 then
                5;
        else
                for a from procname(n-1)+1 do
                        if isprime(a) and isprime(a-2*n) then
                                RETURN(a) ;
                        fi;
                od:
        fi;
end:
seq(A155882(n),n=1..100) ;

Richard J. Mathar, www.strw.leidenuniv.nl/~mathar