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A145043 Primes p for which s=2 is the least positive integer such that sp-t(sp) is a triangular number, where t(n) is the maximal triangular number not exceeding n 2

%I #5 Jul 25 2014 09:31:25

%S 5,17,23,47,53,71,73,127,173,233,251,269,281,347,353,359,431,487,491,

%T 509,541,563,569,593,613,677,743,773,827,857,863,883,929,953,977,1013,

%U 1153,1187,1283,1319,1361,1373,1439,1481,1583,1613,1619,1709,1871,1997

%N Primes p for which s=2 is the least positive integer such that sp-t(sp) is a triangular number, where t(n) is the maximal triangular number not exceeding n

%o (PARI) maxt(n) = {k = 1; while ((t=k*(k+1)/2) < n, k++); if (t == n, t, k--; k*(k+1)/2);}

%o lista(nn) = {forprime(p = 2, nn, if (! ispolygonal(p - maxt(p), 3) && ispolygonal(2*p - maxt(2*p), 3), print1(p, ", ");););} \\ _Michel Marcus_, Jul 25 2014

%Y Cf. A000217, A145032, A145016, A145022, A145023.

%K nonn

%O 1,1

%A _Vladimir Shevelev_, Sep 30 2008

%E More terms from _Michel Marcus_, Jul 25 2014

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Last modified March 28 05:02 EDT 2024. Contains 371235 sequences. (Running on oeis4.)