

A127913


Least k >= 0 such that A001597(n)+k is an even semiprime.


3



3, 0, 2, 1, 6, 1, 7, 2, 2, 9, 10, 1, 6, 1, 9, 6, 2, 9, 6, 2, 1, 11, 6, 9, 2, 3, 1, 22, 5, 18, 2, 9, 10, 1, 18, 5, 10, 1, 14, 13, 6, 18, 5, 18, 1, 10, 15, 13, 10, 1, 18, 25, 26, 2, 9, 6, 1, 14, 6, 7, 9, 9, 2, 1, 18, 1, 18, 2, 9, 2, 21, 9, 6, 5, 22, 11, 1, 2, 1, 18, 5, 10, 1, 2, 13, 42, 1, 18, 5, 1, 2
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..91.


EXAMPLE

A001597(5) = 16. Among 16+0 = 16, 16+1 = 17, 16+2 = 18 = 2*3*3, 16+3 = 19, 16+4 = 20 = 2*2*5, 16+5 = 21 = 3*7 there is no even semiprime, but 16+6 = 22 = 2*11 is an even semiprime. Hence a(5) = 6.
A001597(14) = 121. 121+0 = 121 = 11*11 is not even, but 121+1 = 122 = 2*61 is an even semiprime. Hence a(14) = 1.


PROG

(MAGMA) PP:=[1] cat [ n: n in [2..5184]  IsPower(n) ]; [ k: p in PP  exists(k) {x: x in [0..100000]  IsEven(p+x) and IsPrime((p+x) div 2) } ]; /* Klaus Brockhaus, Apr 09 2007 */


CROSSREFS

Cf. A001597 (perfect powers).
Sequence in context: A034389 A084196 A295041 * A135991 A331422 A279631
Adjacent sequences: A127910 A127911 A127912 * A127914 A127915 A127916


KEYWORD

easy,nonn


AUTHOR

Giovanni Teofilatto, Apr 06 2007


EXTENSIONS

Edited, corrected and extended by Klaus Brockhaus, Apr 09 2007


STATUS

approved



