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A255200
Numbers n such that triangular numbers T(n), T(n+1) and T(n+2) are 3-almost primes.
2
17, 28, 41, 281, 2081, 2801, 4721, 5441, 6196, 12161, 12916, 13996, 20476, 24916, 32321, 32441, 34156, 34961, 40036, 56596, 70996, 73361, 94396
OFFSET
1,1
COMMENTS
Numbers n such that n, n+1 and n+2 are terms in A108815.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
T(17)=A000217(17)=153=3*3*17, T(18)=A000217(18)=171=3*3*19, T(19)=A000217(19)=171=2*5*19.
PROG
(PARI) issemi(n)=bigomega(n)==2
is(n)=if(n%2, if(n%4==1, isprime((n+3)/4) && isprime(n+2) && isprime(n) && issemi((n+1)/2), isprime((n+1)/4) && isprime(n) && isprime(n+2) && issemi((n+3)/2)), if(n%4==2, isprime((n+2)/4) && isprime(n+1) && isprime(n+3) && issemi(n/2), isprime(n/4) && isprime(n+1) && isprime(n+3) && issemi(n/2+1))) \\ Charles R Greathouse IV, Feb 05 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Feb 16 2015
STATUS
approved