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A100916 Sum of a semiprime and its semiprime index is a new semiprime. 4
10, 15, 25, 34, 46, 51, 55, 57, 69, 86, 91, 95, 106, 119, 121, 133, 141, 145, 155, 161, 166, 217, 218, 226, 247, 249, 253, 262, 274, 291, 298, 299, 302, 305, 341, 358, 365, 382, 407, 413, 445, 446, 481, 485, 501, 515, 533, 538, 543, 551, 559, 614, 623, 626 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is the semiprime analog of A061067.

LINKS

Table of n, a(n) for n=1..54.

Eric Weisstein, World of Mathematics, Semiprime.

FORMULA

a(n) = A100466(n) - A100915(n) = A001358(A100915(n)).

EXAMPLE

a(1) = 10 because 10 = semiprime(4) and semiprime(4) + 4 = 14 is

semiprime.

a(2) = 15 because 15 = semiprime(6) and semiprime(6) + 6 = 21 is

semiprime.

MATHEMATICA

Module[{sp=Select[Range[1000], PrimeOmega[#]==2&], len}, len=Length[sp]; Select[ Thread[{sp, Range[len]}], PrimeOmega[Total[#]]==2&]][[All, 1]] (* Harvey P. Dale, Jan 13 2019 *)

CROSSREFS

Cf. A001358, A061067, A100493, A100466, A100467, A100915.

Sequence in context: A091022 A340731 A133372 * A001750 A231643 A276541

Adjacent sequences:  A100913 A100914 A100915 * A100917 A100918 A100919

KEYWORD

easy,nonn

AUTHOR

Ray Chandler, Nov 26 2004

STATUS

approved

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Last modified November 30 12:53 EST 2021. Contains 349419 sequences. (Running on oeis4.)