A045753 -id:A045753 - cp's OEIS frontend

A217837 Numbers n such that 4n - 1 and 4n + 1 are both semiprimes.

14, 23, 30, 36, 40, 46, 51, 54, 55, 59, 62, 72, 75, 76, 80, 82, 85, 98, 103, 104, 113, 118, 129, 132, 134, 136, 138, 145, 167, 170, 172, 174, 195, 198, 204, 225, 240, 264, 270, 275, 280, 284, 285, 287, 292, 301, 314, 318, 329, 336, 337, 339, 346, 347, 348

Offset: 1

Zak Seidov, Oct 12 2012

nonn

This is to semiprimes as A045753 is to primes.

			a(1) = 14 because 56 - 1 = 5*11 and 56 + 1 = 3*19 are semiprimes, and this is the first number having this property.
a(2) = 23 because 92 - 1 = 7*13 and 92 + 1 = 3*31 are semiprimes, and this is the second number having this property.
a(3) = 30 because 120 - 1 = 7*17 and 120 + 1 = 11*11 are semiprimes, and this is the third number having this property.

Zak Seidov, Table of n, a(n) for n = 1..1000

Cf. A045753.

Select[Range[500], PrimeOmega[4# - 1] == 2 && PrimeOmega[4# + 1] == 2 &] (* Alonso del Arte, Oct 12 2012 *)

A174235 The absolute values of (n-th number k such that k4-+1 is twin prime pair minus n-th number m such that m4+2-+1 is twin prime pair).

Original entry on oeis.org

0, 1, 8, 8, 2, 11, 11, 8, 7, 8, 28, 25, 34, 4, 5, 5, 50, 44, 53, 26, 65, 50, 44, 50, 77, 35, 7, 17, 1, 4, 8, 2, 4, 32, 26, 71, 77, 41, 86, 98, 95, 113, 83, 26, 11, 20, 17, 4, 23, 13, 16, 23, 23, 20, 26, 14, 80, 137, 116, 128, 122, 146, 149, 158, 200, 158, 158, 113, 110, 164, 200

Offset: 1

Juri-Stepan Gerasimov, Mar 13 2010

nonn

Cf. A045753, A123986.

a(n)=Abs(A045753(n)-A123986(n)).

Values from a(63) onwards corrected by R. J. Mathar, Apr 16 2010

A174236 n-th number k such that k4-+1 is twin prime pair plus n-th number m such that m4+2-+1 is twin prime pair.

Original entry on oeis.org

2, 7, 22, 28, 52, 79, 85, 106, 127, 148, 202, 235, 250, 304, 325, 409, 460, 472, 493, 550, 595, 664, 682, 694, 727, 775, 841, 877, 937, 970, 1006, 1042, 1060, 1102, 1144, 1225, 1267, 1315, 1414, 1462, 1489, 1513, 1567, 1654, 1675, 1714, 1747, 1774, 1813, 1897

Offset: 1

Juri-Stepan Gerasimov, Mar 13 2010

nonn

Cf. A045753, A123986.

a(n)=A045753(n)+A123986(n).

Corrected (108 replaced by 106) by R. J. Mathar, Apr 16 2010

cp's OEIS Frontend

A217837 Numbers n such that 4n - 1 and 4n + 1 are both semiprimes.

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A174235 The absolute values of (n-th number k such that k4-+1 is twin prime pair minus n-th number m such that m4+2-+1 is twin prime pair).

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A174236 n-th number k such that k4-+1 is twin prime pair plus n-th number m such that m4+2-+1 is twin prime pair.

Views

Author

Keywords

Crossrefs

Formula

Extensions

cp's OEIS Frontend

A217837 Numbers n such that 4n - 1 and 4n + 1 are both semiprimes.

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Author

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Mathematica

A174235 The absolute values of (n-th number k such that k*4-+1 is twin prime pair minus n-th number m such that m*4+2-+1 is twin prime pair).

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Author

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Extensions

A174236 n-th number k such that k*4-+1 is twin prime pair plus n-th number m such that m*4+2-+1 is twin prime pair.

Views

Author

Keywords

Crossrefs

Formula

Extensions

A174235 The absolute values of (n-th number k such that k4-+1 is twin prime pair minus n-th number m such that m4+2-+1 is twin prime pair).

A174236 n-th number k such that k4-+1 is twin prime pair plus n-th number m such that m4+2-+1 is twin prime pair.