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A176804 Lesser of twin primes p such that p = semiprime(k)/2 and p + 2 = semiprime(k+2)/2 for some integer k. 0
3, 11, 17, 41, 179, 197, 239, 281, 311, 419, 431, 461, 521, 599, 641, 821, 827, 857, 1019, 1049, 1061, 1091, 1151, 1229, 1289, 1319, 1427, 1481, 1487, 1607, 1667, 1697, 1721, 1871, 1877, 1931, 1997, 2027, 2081, 2111, 2141, 2309, 2339, 2591, 2687, 2789 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..46.

EXAMPLE

3 is a term because 3 = semiprime(2)/2 = 6/2 and 3 + 2 = 5 = semiprime(2+2)/2 = 10/2.

MAPLE

From R. J. Mathar, Apr 27 2010: (Start)

isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc:

A001358 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if isA001358(a) then return a; end if; end do: end if ; end proc:

A174956 := proc(p) for n from 1 do if A001358(n) = p then return n; elif A001358(n) > p then return 0 ; end if; end do: end proc:

A001359 := proc(n) option remember; if n = 1 then 3; else for a from procname(n-1)+2 by 2 do if isprime(a) and isprime(a+2) then return a; end if; end do: end if; end proc:

for i from 1 to 400 do p := A001359(i) ; n := A174956(2*p) ; n2 := A174956(2*p+4) ; if n > 0 and n2 >0 and n2=n+2 then printf("%d, ", p) ; end if; end do: (End)

CROSSREFS

Sequence in context: A100567 A270225 A262275 * A078116 A245045 A127996

Adjacent sequences:  A176801 A176802 A176803 * A176805 A176806 A176807

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Apr 26 2010

EXTENSIONS

Corrected (541 replaced by 521, 1047 replaced by 1049, 1741 replaced by 1721) by R. J. Mathar, Apr 27 2010

STATUS

approved

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Last modified April 23 03:26 EDT 2019. Contains 322380 sequences. (Running on oeis4.)