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A115560 Twin prime pairs k-1 and k+1 such that the squares of both are present in A115557. 2
11, 13, 29, 31, 197, 199, 239, 241, 419, 421, 659, 661, 881, 883, 1019, 1021, 1061, 1063, 1481, 1483, 1877, 1879, 3167, 3169, 3821, 3823, 4019, 4021, 4049, 4051 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..30.

FORMULA

The commutator [sigma, tau] is zero and a(n) is the square root of special prime solutions. These solutions are twin primes. Both twins are displayed.

PROG

ta={{0}}; tb={{0}}; Do[s=DivisorSigma[1, DivisorSigma[0, n]]; s1=DivisorSigma[0, DivisorSigma[1, n]]; If[Equal[s-s1, 0]&&IntegerQ[Sqrt[n]&&PrimeQ[Sqrt[n]]], Print[n]; ta=Append[ta, n]; tb=Append[tb, Sqrt[n]]], {n, 1, 100000000}] ta=Delete[ta, 1]; tb=Delete[tb, 1]; ni=Intersection[tb, 2+tb]; Union[ni, ni-2]

CROSSREFS

Cf. A000005, A000203, A076360, A076361, A062068, A062069, A115557, A115558, A115559.

Sequence in context: A140567 A232880 A117314 * A045466 A158759 A107645

Adjacent sequences:  A115557 A115558 A115559 * A115561 A115562 A115563

KEYWORD

nonn

AUTHOR

Labos Elemer, Jan 25 2006

STATUS

approved

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Last modified May 23 12:45 EDT 2017. Contains 286915 sequences.