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A176544 Primes of the form semiprime(k)/sum of digits of semiprime(k). 1
7, 37, 19, 67, 19, 19, 37, 37, 73, 37, 73, 337, 367, 163, 73, 109, 127, 73, 109, 163, 127, 181, 163, 433, 181, 163, 199, 181, 271, 163, 199, 199, 271, 271, 397, 307, 307, 487, 379, 541, 433, 577, 397, 271, 631, 433, 379, 487, 919, 1459, 541, 937, 811, 631, 991 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = p = A001358(n)/A175013(n).
a(n) = A001358(A176543(n))/A175013(A176543(n)). - R. J. Mathar, Apr 26 2010
EXAMPLE
7 is a term because 7 = 21/(2+1);
37 is a term because 37 = 111/(1+1+1).
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 4000 do r := A001358(n)/A175013(n) ; if type(r, 'integer') then if isprime(r) then printf("%d, ", r) ; end if; end if; end do: # R. J. Mathar, Apr 26 2010
MATHEMATICA
Select[#/Total[IntegerDigits[#]]&/@Select[Range[30000], PrimeOmega[#]==2&], PrimeQ] (* Harvey P. Dale, Aug 10 2023 *)
CROSSREFS
Cf. A001358 (semiprimes), A007953 (sum of digits), A175013, A176543.
Sequence in context: A120106 A240274 A129737 * A281994 A246603 A043374
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
More terms from R. J. Mathar, Apr 26 2010
STATUS
approved

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Last modified March 29 05:43 EDT 2024. Contains 371264 sequences. (Running on oeis4.)