A172487 - OEIS

A172487

Lesser of twin primes in A172240.

3, 17, 29, 41, 71, 101, 137, 149, 191, 197, 239, 269, 281, 311, 419, 431, 461, 521, 569, 599, 617, 641, 659, 809, 821, 827, 857, 881, 1031, 1049, 1061, 1091, 1151, 1229, 1277, 1289, 1301, 1427, 1451, 1481, 1607, 1667, 1697, 1721, 1787, 1871, 1877, 1931, 1949, 1997

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

For a(n) > 3, the first differences of the sequence are divisible by 6. (Is this a conjecture or a theorem?)

LINKS

Table of n, a(n) for n=1..50.

FORMULA

A001359 INTERSECT A172240.

MAPLE

isA001359 := proc(p) isprime(p) and isprime(p+2) ; end proc:

isA000430 := proc(p) if isprime(p) then true; else if issqr(p) then isprime(sqrt(p)) ; else false; end if; end if; end proc:

isA181669 := proc(p) if isprime(p) and (p mod 6)= 5 then if numtheory[bigomega](p-1) =2 and isA000430(p+2) then true; else false; end if; else false; end if ; end proc:

isA172240 := proc(n) isprime(n) and not isA181669(n) ; end proc:

isA172487 := proc(n) isA172240(n) and isA001359(n) ; end proc:

for n from 2 to 2000 do if isA172487(n) then printf("%d, ", n) ; end if; end do:

CROSSREFS

Cf. A173176, A172240, A181669, A181602.

Sequence in context: A105912 A249374 A106085 * A007490 A173587 A022887

Adjacent sequences: A172484 A172485 A172486 * A172488 A172489 A172490

KEYWORD

nonn,easy

AUTHOR

Giovanni Teofilatto, Nov 21 2010

STATUS

approved