A131866 - OEIS

A131866

Distance of n-th semiprime to nearest square.

0, 2, 0, 1, 2, 1, 4, 3, 0, 1, 3, 2, 1, 2, 3, 3, 0, 2, 6, 7, 6, 2, 1, 5, 7, 4, 1, 4, 5, 6, 9, 7, 6, 5, 6, 10, 6, 3, 2, 0, 1, 2, 8, 11, 10, 3, 2, 1, 1, 2, 11, 11, 10, 8, 3, 0, 8, 9, 13, 11, 9, 2, 5, 6, 7, 9, 10, 13, 12, 11, 10, 8, 7, 6, 4, 1, 10, 12, 9, 7, 3, 2, 3, 6, 9, 11, 15, 11, 2, 0, 2, 6, 9, 10, 12

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OFFSET

1,2

COMMENTS

This to semiprimes A001358 as A047972 is to primes A000040.

For each semiprime, find the closest square (preceding or succeeding); subtract, take absolute value.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n)=A053188(A001358(n)) (corrected by R. J. Mathar, Nov 19 2007).

EXAMPLE

a(1) = 0 because the first semiprime is 4, which is a square.