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 A056562 Number of primes which are the difference between two triangular numbers, where the smaller is the n-th triangular number. 2
 1, 1, 2, 0, 2, 1, 1, 1, 1, 0, 2, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 2, 0, 0, 1, 0, 0, 2, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 2, 0, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 2, 1, 0, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 2, 0, 0, 1, 0, 0, 2, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n)=2 if both n+1 is prime and 2n+3 is prime, =1 if one of n+1 and 2n+3 is prime, =0 if neither are primes. EXAMPLE a(4)=2 because 4th triangular number is 10 and both 15-10=5 and 21-10=11 are primes. CROSSREFS Cf. A000217, A001227, A056563, A056564. Sequence in context: A112553 A026610 A094451 * A135220 A068320 A111330 Adjacent sequences:  A056559 A056560 A056561 * A056563 A056564 A056565 KEYWORD nonn AUTHOR Henry Bottomley, Jun 27 2000 STATUS approved

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