A377788 - OEIS

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A377788

a(n) is the smallest prime not yet in the sequence such that pi(a(n)) divides the sum a(n) + n, or -1 if no such prime exists.

2, 31, 3, 5, 7, 3067, 89, 307, 11, 3049, 13, 313, 19, 23539, 3023, 269, 223, 17, 251, 23497, 29, 23, 37, 41, 911, 59, 43, 47, 61, 1303051, 79, 73, 107, 2647, 811, 109, 113, 2671, 2663, 2683, 787, 1303091, 53, 2609, 8059, 2621, 67, 2591, 71, 23431, 2693, 2699

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OFFSET

1,1

COMMENTS

The defining question is, what is the next term after a(1) = 2, that must be the smallest odd prime not yet used, to which adding that term's index n, that sum is divisible by the index of that fitting prime number, pi(a(n))?

LINKS

Table of n, a(n) for n=1..52.

EXAMPLE

a(2) = 31 because 31 + 2 = 33, and since 31 is the 11th prime, pi(31) = 11, which divides 33, and there is no smaller prime than 31 which satisfies that condition.

a(7) = 89 because 89 + 7 = 96, and since 89 is the 24th prime, pi(89) = 24, which divides 96, and there is no smaller prime than 89 which satisfies that condition.

CROSSREFS

Cf. A000040, A000720.

Sequence in context: A159578 A376416 A221192 * A178194 A069460 A352959

Adjacent sequences: A377785 A377786 A377787 * A377789 A377790 A377791

KEYWORD

sign

AUTHOR

Tamas Sandor Nagy, Nov 07 2024

STATUS

approved