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A117429 Semiprime nearest to 5^n. In case of a tie, choose the smaller. 1
4, 4, 25, 123, 626, 3127, 15623, 78123, 390623, 1953122, 9765627, 48828127, 244140623, 1220703121, 6103515629, 30517578127, 152587890617, 762939453119, 3814697265623, 19073486328122, 95367431640623 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Distance from 5^n to the nearest semiprime.

LINKS

Table of n, a(n) for n=0..20.

FORMULA

a(n) = 5^n + A117430(n). a(n) = 5^n + Min{k such that A001358(i) + k = 5^n}.

EXAMPLE

a(0) = 4 because 5^0 + 3 = 4 = A001358(1) and no semiprime is closer to 5^0.

a(1) = 4 because 5^1 - 1 = 4 = A001358(1) and no semiprime is closer to 5^1.

a(2) = 25 because 5^2 + 0 = 25 = A001358(9), no semiprime is closer to 5^2.

a(3) = 123 because 5^3 - 2 = 123 = 3 * 41 = A001358(42), no semiprime is closer.

a(4) = 626 because 5^4 + 1 = 626 = 2 * 313, no semiprime is closer.

a(5) = 3127 because 5^5 + 2 = 3127 = 53 * 59, no semiprime is closer.

a(6) = 15623 because 5^6 - 2 = 15623 = 17 * 919, no semiprime is closer.

a(7) = 78123 because 5^7 - 2 = 78123 = 3 * 26041, no semiprime is closer.

a(8) = 390623 because 5^8 - 2 = 390623 = 73 * 5351, no semiprime is closer.

a(9) = 1953122 because 5^9 - 3 = 1953122 = 2 * 976561, no semiprime is closer.

a(10) = 9765627 because 5^10 + 2 = 9765627 = 3 * 3255209, no semiprime closer.

CROSSREFS

Cf. A117416 = Semiprime nearest to 3^n, A117405 = Semiprime nearest to 2^n, A117387 = Prime nearest to 2^n.

Cf. A000079, A001358, A117387, A117405, A117406, A117416, A117430.

Sequence in context: A269097 A171633 A221276 * A132650 A112953 A110139

Adjacent sequences:  A117426 A117427 A117428 * A117430 A117431 A117432

KEYWORD

easy,nonn,less

AUTHOR

Jonathan Vos Post, Mar 14 2006

STATUS

approved

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Last modified May 30 03:31 EDT 2017. Contains 287305 sequences.