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A176543 Numbers k such that semiprime(k)/sum of digits of semiprime(k) is prime. 1
7, 36, 44, 63, 68, 79, 128, 148, 157, 192, 244, 303, 323, 335, 410, 421, 475, 483, 535, 606, 616, 669, 776, 849, 862, 868, 947, 964, 986, 1039, 1046, 1256, 1264, 1403, 1406, 1422, 1579, 1700, 1733, 1874, 1971 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..41.

FORMULA

A001358(a(n))/A175013(a(n)) is prime.

EXAMPLE

7 is a term because 7 (prime) = 21/3 = semiprime(7)/sum of digits of semiprime(7);

36 is a term because 37 (prime) = 111/3 = semiprime(36)/sum of digits of semiprime(36).

MAPLE

A175013 := proc(n) A007953(A001358(n)) ; end proc: A007953 := proc(n) add(d, d=convert(n, base, 10)) ; end proc: for n from 1 to 2000 do r := A001358(n)/A175013(n) ; if type(r, 'integer') then if isprime(r) then printf("%d, ", n) ; end if; end if; end do: # R. J. Mathar, Apr 26 2010

CROSSREFS

Cf. A001358 (semiprimes), A007953 (sum of digits), A175013.

Sequence in context: A197555 A028389 A041603 * A018199 A063168 A163683

Adjacent sequences:  A176540 A176541 A176542 * A176544 A176545 A176546

KEYWORD

nonn,base,less

AUTHOR

Juri-Stepan Gerasimov, Apr 20 2010

EXTENSIONS

More terms from R. J. Mathar, Apr 26 2010

STATUS

approved

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Last modified April 13 22:30 EDT 2021. Contains 342941 sequences. (Running on oeis4.)